Calculating Latitude and Longitude Changes

hello everyone welcome back in this video i&#39;ll be talking about how to find the difference between two given latitudes or two given longitudes so this is also known as the change in longitude or the change in latitude now i&#39;ll talk about everything that can be related to this topic i&#39;ll start from the very basics of what is a latitude what is a longitude what is the equator what is the green which prime radian how do we measure longitudes how do we measure latitudes what is the reason why do we need to calculate the change in longitude of the change in latitude everything so if you want to know everything about latitudes and longitudes this should be the video for you i&#39;m sure this is going to be helpful so let&#39;s dive into it now before i start talking about what is change in longitude or what is the change in latitude i want to start with the basics so i want you to build your basics first so let&#39;s start by how do we name latitudes and longitudes because if you understand this if your basics are strong you&#39;ll be able to find the change in latitudes or change in longitudes very very easily i feel that that is just a very very small part of this video so let&#39;s start with longitudes so what are longitudes longitudes are just vertical lines which are running from one pole to the other pole now in this diagram all the blue lines and the one red line are the longitudes okay now there&#39;s a place called greenwich which is located in london it&#39;s this place and the longitude which passes through greenwich which will be this longitude is called the greenwich prime meridian meridian is just another name for longitude so what is this greenwich prime meridian so this particular meridian is known as the datum meridian so what this means is that the meridians which are to the left or to the right of this greenwich prime meridian will be named according to the position or the angle they make with the greenwich prime meridian i&#39;ll explain all this so what you need to know is that this meridian is the datum meridian right this is the main meridian now all the meridians which are to the west of the greenwich prime meridian are termed west and all the meridians to the east of the greenwich prime meridian are termed as east okay and since the greenwich prime meridian lies in the center it is known as zero degrees east slash west okay very easy so when i was talking about these meridians i said that the meridians are named according to the angle they make with the data meridian so what i mean is this so if you look at this diagram we can see that this is the greenwich prime meridian and there is a place b which lies on this medium yeah so this is actually the top down view of the earth so this is the north pole now i think it will be much more easier for you to visualize so this is the top down view of the earth the red line is the green ridge prime meridian and there&#39;s a place b the longitude which passes through b is the green line now if we measure the angle between the greenwich prime meridian and the meridian that is passing through point b we&#39;ll get this angle right let&#39;s say this is 45 degrees angle so this meridian which was passing through point b will be the 45 degree east meridian why is this east because obviously it is to the east of the greenwich primary do you understand now i&#39;ll take another example so let&#39;s say there was a place c over here okay there was a place c and now if i make a longitude which is passing through c it will be something like this now the angle this makes with the greenwich prime meridian is 90 degrees so what we can say is that this longitude is 90 degree west longitude west because it is to the left of the greenwich prime meridian or it is to the west of the greenwich primary okay so this is the 90 degree west meridian if i talk about this this will probably be 130 degree west and if i keep continuing the maximum which i can get is this so the angle this meridian makes with the greenwich prime meridian will be 180 degrees so that meridian is the 180 degree meridian it is actually the anti-meridian of the greenwich primary what do you mean by anti-meridian anti-meridian is the meridian that is right behind the main meridian so if this was 0 degrees east west that will be 180 degree east west so that is the maximum value a longitude can have so the maximum value of a longitude is 180 degree east-west okay why is it east-west both because it is lying right between the east and the west meridians if i go over here this will be 90 degree east this will be 130 degrees this will be 140 150 160 170 and this main one will be 180 degree east or west because it is being shared between both the east and the west medians so these are longitudes i hope you understood the concept behind this now if we look at this view of the graticule we can see that this red line is the primary idiom now this line which is to the right will be probably 30 degree east since it&#39;s to the east this will be 60 degrees this line which is to the left will be 30 degree west longitude this will be maybe 60 degree west and so on right so that is how we name or that is how we measure the longitudes so it is the angle the longitude makes with the prime meridian perfect now let&#39;s look at what are latitudes so latitudes are parallel lines on either sides of the equator so all the blue lines and the one red line you can see are the parallels of latitudes so these are nothing but small circles so if you have watched the previous video you would know what are small circles and what are great circles so i told you there also that parallels of latitude are nothing but small circles so the equator is a great circle and small circles around the equator on either sides up to the poles are parallels of latitudes so the datum of these lines is the equator now the equator is known as zero degree north south latitude and any latitude above the equator is termed north and any latitude below the equator in the southern hemisphere are termed as south so this is the importance of the datum the datum decides what value has to be given to what latitude right now how do we measure these latitudes so if you look at this diagram now this is the straight on view of the earth so this is the equator and there is a place a on the surface of the earth so this point a lies on this latitude yeah so what we do is that we take a line from a which is a point on the earth we take that line to the center of the earth and we measure the angle it is making with the equator so this angle which is the angle between the equator and the line joining the place to the center of the earth is taken into consideration while naming the latitude so we can see that this angle is 40 degrees so what we can say is that this latitude is 40 degree north latitude why not because it is north of the equator and why 40 degrees because it is making 40 degrees with the equator right so now if i take a point b which is here so let&#39;s say this is the latitude and the next thing we do is that we join this point to the center of the earth and we measure the angle between this line and the equator so it turns out that this angle is 60 degrees so this latitude will be 60 degrees south latitude okay now if i consider the poles so if i talk about the north pole if i draw a line from the north pole to the center of the earth i can see that this makes an angle of 90 degrees so the latitude at the north pole will be 90 degree not latitude and similarly the latitude on the south pole will be 90 degrees south latitude because it&#39;s going to make 90 degree with the equator perfect so the maximum value a latitude can get is 90 degree north or 90 degrees south and the equator which is the datum is zero degrees not south latitude perfect now these latitudes and longitudes which we discussed so far are given in degrees like it was 90 degree note 60 degree south 40 degree north or if we look at the longitudes we talked about 60 degree east 60 degree west and so on but we can also get latitudes and longitudes in degrees minutes and seconds which can be something like this so we write it like this so this means minutes and this is seconds and obviously this sign is for degrees yep so since i&#39;ve talked about minutes and seconds i want you guys to know about these very basic very small conversions so the first one is that one degree is equal to 60 minutes right and the second one is that one minute is equal to 60 seconds yeah very easy so i want you to keep these two conversions in mind so one degree equals 60 minutes and each minute equals 60 seconds it&#39;s similar to what we use in time now how do we plot these points on the earth so if i am given this coordinate how do i plot it on the earth i&#39;ll tell you it&#39;s very easy so to plot this particular coordinate on a map i need two things to plot the latitude i need the equator which is the datum and to plot the longitude i need the prime meridian which is the datum for longitudes so let&#39;s say this is the equator and this is the prime meridian now for 20 degrees north i&#39;ll go 20 degrees towards the north from my equator so let&#39;s say this was 5 degrees 10 degrees 15 degrees 20 degrees so this is my 20 degrees north latitude now from here i&#39;ll go 45 degrees towards the east so this is 45 degrees towards the east from my prime meridian so prime meridian was this vertical yellow knight so now i&#39;ll start going towards the right so this was 5 degrees east 10 degrees 15 20 25 30 35 40 45 so this is my 45 degree east latitude now this point over here will be the point that i&#39;m looking for so this will be 20 degree north 45 degree east point so do you understand first i went 20 degrees up from the equator then i went 45 degrees towards the right which is towards the east from my prime medium and this point is what i was looking for so that is how we plot coordinates now if you understood whatever i have talked about till now believe me the other half of the video will just be a cakewalk for you i know a lot of you would already know whatever i&#39;ve talked about right now but i want you guys to realize how important it is for you to know all this so now coming back to my initial question why do we need to find the difference between two latitudes or two longitudes why do we need to find the change in longitudes or the change in latitudes why so let&#39;s say we are to find the distance between two places on the earth with these coordinates so the first place is 10 degrees not 30 degree west and the second place is 10 degree north 62 degrees east so the first thing i want to do is to plot these points to know where these points are so that is the equator prime meridian for the first point i&#39;ll go 10 degrees north let&#39;s say it&#39;s here and 30 degrees west west is to the left so 30 degree west probably here so this is my point number one now the second point 10 degrees north which is again this point and 62 degrees east so now this will be to the right somewhere here so my point number two will be over here right now i want to find the distance between these two points so what i see is that both of these points are lying on the same latitude and this latitude is 10 degrees north the other thing that i can see is that the two longitudes are different so this point was on 30 degrees west longitude and the second point was on 62 degrees east longitude so if i want to find the distance between the two points obviously i need to find the distance between these two longitudes first and this distance between these two longitudes is known as the change in longitude so the reason we find change in longitude or the change in latitude is to find the distance between the two points right so here in this case we saw that both the points are on the same latitude the longitudes are different if someone wants me to calculate the distance between the two points i will definitely need to find the distance or the change of longitude that has taken place between these two points and that is where we find the change in longitude similarly if i look at this example now so here we have two points and if we are asked to find the distance between the two points the first thing that i&#39;ll do is plot them so this is the primary median this is the equator so for the first point it is 51 degrees north somewhere here 12 degrees west so 12 degree west will be somewhere here so this is my first point and the second point is 6 degrees north somewhere here and 12 degrees west 12 degree west will be somewhere here so this is my point number two now in this example what i can see is that the longitude is same so both of these points are on 12 degrees north longitude the latitudes are different so the point number one was 51 degree north and the second point was at six degree north now if someone wants me to find the distance between point one and point two i will definitely need to know about the change of latitude that is taking place between the two points right first point was at six degree north and the second point was at 51 degrees north so i have to know that there is a difference of 45 degrees between both of these points only then i&#39;ll be able to calculate the distance between them right so this is where change in longitude or change in latitude comes into play so this is change in latitude so now i hope you understood why we need to calculate the change in longitude or the change in latitudes perfect next i want to talk about basic addition and subtraction of degrees i don&#39;t know how good you guys are at this already but it&#39;s my duty to teach it so here it is so there are two latitudes given one and two and i want to add both of them so i&#39;ll tell you how i do it the first step is to write everything separately first i&#39;ll write the first latitude is 22 degrees 15 minutes and 25 seconds now below this i&#39;ll write the second latitude which is 21 degrees 10 minutes and 35 seconds and i want to add these so this was the first step to write everything separately so that i can add degrees to degrees minutes to minutes seconds to seconds so the answer will be 60 seconds 25 minutes and 43 degrees right now what we can see from here is that 60 seconds can also be written as one minute right so what we do is we take one minute and add to the 25 minutes so it becomes 26 minutes and 43 degrees with zero seconds so this is the answer 43 degrees 26 minutes zero seconds so why zero seconds because we took the 60 seconds converted it to minutes and added 1 minute to the already 25 minutes we had so that is how we add two latitudes now similarly if i wanted to subtract 10 degrees 25 minutes 50 seconds from 40 degrees 15 minutes and 34 seconds what i do is write everything separately number one so it will be 40 degrees 15 minutes 34 seconds and below it 10 degrees 25 minutes 50 seconds i want to subtract perfect so this will be 30 degrees and oops 15 is smaller than 25 similarly 34 is smaller than 50. now what do i do so one thing at a time first we see that 15 minutes is smaller than 25 minutes so i cannot subtract 25 from 15 i&#39;ll have to do something so what i do is that i take one degree convert it to minutes which will be 60 minutes and i put it over here so what happens is that this 40 becomes 39 degrees and i get 15 plus 60 which is equal to 75 minutes over here right now i see 75 is bigger than 25 so i can subtract 25 from 75 minutes next i see that 34 seconds is smaller than 50 seconds so what do i do i do something similar so i take one minute and convert it to 60 seconds right so this 75 becomes 74 minutes and this 34 becomes 34 plus 60 which is 94 seconds so if i look at it my new equation will be 39 degrees 74 minutes 94 seconds minus sign 10 degrees 25 minutes and 50 seconds so i can easily subtract now the answer will be 44 seconds 49 minutes so this will be my answer which is 29 degrees 49 minutes and 44 seconds so this is how we add and subtract latitudes and longitudes now good news for some people so if you are allowed to carry a scientific calculator all this is gonna be easy for you as you can directly put in degrees minutes and seconds to add or subtract in your scientific calculator now if i use a scientific calculator for this same example i won&#39;t have to do anything i just put the values and i&#39;ll get the answer so i&#39;ll put 40 press this key which is for the degrees i&#39;ll put 15 press this key again now it&#39;s acting as the minute scheme and i&#39;ll press 34 press this key again which is for the seconds now i&#39;ll use the subtract function and put the next value which is 10 degrees 25 minutes and 50 seconds and if i look at the answer the answer is 29 degrees 49 minutes and 44 seconds so you see how easy it becomes with the scientific calculator yeah so if you&#39;re allowed to use a scientific calculator feel free to use it but what i personally feel is that everyone should be able to calculate this manually because anyone can do it with a calculator right you should know how to do it manually just end of story perfect so now you know what are latitudes what are longitudes how do we measure latitudes how do we measure longitudes you know how to add how to subtract units in degrees minutes and seconds so perfect finding the change in latitudes or the change in longitudes will be very very easy for you now so now let&#39;s look at how to find the change of latitude or the change in longitudes so in the exam there will be direct questions on just to find the change in longitude or the change in latitude number one next type of questions will be for you to find the distance between two given points and you&#39;ll see that when you&#39;re asked to find the shortest distance between two given points which is the departure you&#39;ll obviously have to find the change in longitude so these are the two type of questions you can expect in the exams okay now when you&#39;re asked to find the change in longitude or the change in latitude between two given lats or two given longs you&#39;re supposed to give a value in degrees minutes and seconds of the shortest distance between the two given latitudes or longitudes so just keep this in mind that you have to find the shortest distance between those two latitudes or those two longitudes right perfect now let&#39;s learn by examples so in the first example it asks us to find the sheila at between 55 degrees 29 minutes south to 31 degrees 48 minutes south so this is my equator prime meridian for the first point it says 55 degrees 29 minutes south so i go 55 degrees 29 minutes south which is somewhere here so this will be one latitude which is 55 degrees 29 south and the second latitude is 31 degrees 48 minutes south so it will be somewhere here it&#39;s 31 degrees 48 and it&#39;s south and this was the equator which is 0 degrees north south so what i have to find is the change between these two latitudes so the red area it&#39;s very easy so you see this was 55 degrees something and this was 31 degrees something so now do you think that if i subtract 31 degrees 48 minutes from 55 degrees 29 minutes the thing i&#39;ll be left with will be this part right and that is exactly what i have to find so what i&#39;ll do is i&#39;ll take 55 degrees 29 minutes and i&#39;ll subtract 31 degrees 48 minutes from this so if i use my calculator i&#39;ll put 55 degrees 29 minutes minus 31 degrees 48 minutes and the answer comes out to be 23 degrees 41 minutes right so this is the change in latitude now if i put the north south values in this so it was 55 degrees south and 31 degrees south now i want you to read the question again so in the question it asks what is the change in latitude between 55 degrees to 31 degrees right it said a value from this to this so that means that i&#39;m moving from 55 degrees towards 31 degrees which means that i&#39;m moving towards the north right 31 degrees is north of 55 degrees so i&#39;ll put a value north over here now the value of change in latitude is complete so it is always complete when i give a direction so my change in latitude is 23 degrees 41 minutes north perfect now let&#39;s look at another example so in this example it says that what is the change in latitude between 26 degrees 57 minutes south to 14 degrees 25 minutes north okay so the first thing here again is that we&#39;ll plot these points so this is my prime meridian this is the equator which is zero degrees north slash south the first latitude is 26 degrees 57 minutes south so let&#39;s say it&#39;s somewhere here so this is 26 degrees 57 minutes south and the second latitude is 14 degrees 25 minutes north so it will be somewhere here north of the equator so this is 14 degrees 25 minutes north now i want to find the change in latitude between 26 degrees to 14 degrees so i want to find this value it&#39;s very easy again so you see this was 26 degrees 57 minutes right and this was 14 degrees 25 minutes to find the red arrow i just add both of these i&#39;ll put 26 degrees 57 minutes add 14 degrees 25 minutes to it what do i get i get 2 82 minutes and 40 degrees now obviously i cannot leave it in 82 minutes so it will be 41 degrees and 22 minutes right because the maximum value of a minute is 60. i cannot go above 60 minutes if i&#39;m exceeding 60 minutes then i&#39;ll have to subtract 60 from this and add 1 to the degrees right because 1 degree was 60 minutes perfect so it is 41 degrees and 22 minutes now for the north south value it was 26 to 14 that means i am going towards the north so i&#39;ll put north and this is my change in latitude between 26 degrees 57 minutes south to 14 degrees 25 minutes north perfect so i hope you understood the point here now a small trick so if both the latitudes are in the same hemisphere we usually subtract one from another like in this diagram if we were talking about 30 degrees south and 60 degree south to find this area we&#39;ll have to subtract 30 degrees from 60 degrees right similarly if i was talking in the northern hemisphere it was 30 degrees and let&#39;s say this is 15 degrees so to find this change i&#39;ll have to subtract 15 degrees from 30 degrees right that is what is written in this slide so it says north not subtract south south subtract which was this case and it says not south add so what this means is that if we were talking about two latitudes let&#39;s say 15 degrees and 15 degrees now i want to find this region what will i do obviously i&#39;ll add this 15 to this 15 and i&#39;ll get 30 degrees so this will be my change in latitude so for north south we have to add so this is a very basic trick you can use to find the change in latitudes now let&#39;s look at some change in longitude examples so the first example here asks us that what is the change in longitude between 82 degrees 35 minutes east to 132 degrees 42 minutes east so the first thing we do is plotting now to plot for change in longitudes there is a separate diagram so this is the earth this is the north pole this is the greenwich prime meridian which is zero degrees east west and this is its anti-meridian which is 180 degree east west so you remember this diagram from the beginning it&#39;s the same now if i&#39;m going towards the right it is east if i&#39;m going towards the left it is west perfect so the first longitude is 82 degrees 35 minutes east so it will be this longitude 82 degrees 35 minutes east so if you remember we take the angle between the longitude and the prime reading and it should be equal to the name of the longitude so this angle would be probably 82 degrees right so the yellow one is the first longitude and the second longitude is 132 degrees 42 minutes east so it will somewhere be over here says 132 degrees 42 minutes east this is number two this angle also looks more like 132 degrees right so i&#39;ve plotted both of the longitudes correctly now what i want to find is the change or the difference between these two so this was 132 this was 82 if i subtract 82 from 132 i will be left with this right so i&#39;ll write 132 degrees 42 minutes east minus 82 degrees 35 minutes east zero seven minutes 50 degrees so the answer will be 50 degrees 7 minutes you know if i talk about whether it will be east or west so we go back to the question it says between 0 8 2 degrees and 1 3 2 degrees so that means we are going from this longitude to this longitude so we&#39;ll just look at these arrows now so looking at these arrows we see that we&#39;re going in the direction of east right so i&#39;ll put east over here so this is my change in longitude between 82 degrees 35 minutes east and 132 degrees 42 minutes east this is also very straightforward very easy perfect now let&#39;s look at the second example so it&#39;s asking us what is the change in longitude between 0 0 4 degrees 32 minutes west to 0 1 0 degrees 15 minutes east now again i&#39;ll draw the same diagram for change in longitude this is the earth north pole prime meridian anti-meridian this side is east and this side is west okay so the first longitude is four degrees 32 minutes west so it will be somewhere very close over here this will be zero zero 4 32 west and the other longitude is 10 degrees 15 minutes east so it will be on this side now 10 degrees 15 minutes east and what i have to find is this difference between the two longitudes now if you see that even this is the change in longitude right this is also a difference between the two why am i always finding this distance so the answer to this is because i want to find the shortest arc so this is the shortest arc so if i want to go from 4 degrees west to 10 degrees west obviously i&#39;ll take this path right i won&#39;t go all the way in this path right i want the shortest distance so that&#39;s why i&#39;m finding the shortest arc so how do i find this i see that this is 10 degrees 15 minutes east and this is 4 degrees 32 minutes west so i will add both of these up and get the required change in longitude so it will be 0 zero degrees 15 minutes east plus zero zero four degrees 32 minutes west the answer will be 47 minutes zero and four degrees and in the question it says that we are going from zero zero four to zero one zero so it would be zero zero four two zero one zero that means going in the eastward direction so i can put east over here and this is my change in longitude 14 degrees 47 minutes east perfect now the last example asks us to find the change in longitude between 140 degrees 27 minutes east to 160 degrees 54 minutes west so again we&#39;ll make the earth the north pole prime meridian anti meridian the direction arrows and we plot the points so the first point is 140 degree east so since this is 180 degrees 140 will be somewhere here 140 degrees 27 minutes east and the next point is 160 degrees 54 minutes west so even this point will be close to the 180 degree east west line so let&#39;s say it&#39;s this so it is 160 degrees 54 minutes west perfect so now i want to find this difference i don&#39;t want to find this difference because this is a longer arc i always look for the shortest arc so this one can be a bit tricky for you if you don&#39;t pay attention so this was 180 degrees right that is the prime reading now this is 140 degrees and 27 minutes so if i want to find this much area can i subtract 140 from 180 will i get this red difference yeah i can so i&#39;ll write 180 degrees minus 140 degrees 27 minutes and i&#39;ll find this now similarly on the other side this was again 180 degrees yeah and this was 160 degrees 54 minutes so to find this area can i subtract 160 degrees 54 minutes from 180 degrees yeah i can get this red arc as well so for that i&#39;ll write 180 degrees minus 160 degrees 54 minutes and i&#39;ll find that and to find the total i&#39;ll have to add both of these up so when i add both of these up what i&#39;ll get is this value so what i did was i subtracted 140 from 180 i got this area and i subtracted 160 from 180 to get this area then i added both of these up to get the total area so this is my plan so for this i&#39;ll use the calculator it&#39;s much faster so i&#39;ll take 180 degrees subtract 140 degrees 27 minutes from it i&#39;ll get 39 degrees 33 minutes and get 39 degrees 33 minutes and for the next one it is 180 degrees minus 160 54. this comes out to be 19 degrees six minutes so after adding both of these up i&#39;ll get 58 degrees 39 minutes so this is my change in longitude now in the question it says that i am going from 140 to 160 that means i am going from here to here so this will be the arrow and this arrow is again in the eastward direction so i&#39;ll put east over here so the change in longitude between 140 degrees 27 minutes east and 160 degrees 54 minutes west is 58 degrees 39 minutes east right 160 degrees is east of 140 degrees because we&#39;re going towards the right and that arrow is towards the east so perfect i think now you&#39;ll be able to find the change in longitudes and latitudes very very easily just keep in mind that we always go for the shortest arc while finding the change in longitudes and don&#39;t forget to draw this diagram so whenever you&#39;re finding the change in longitudes or the change in latitudes always draw diagrams it helps you imagine what&#39;s going on and whenever you draw the diagrams never forget these arrows because these arrows will help you understand this part of the answer and a change in longitude or a change in latitude is incomplete without a direction so always draw these arrows always draw the diagram and never forget to write the direction of the change in latitude or the change in longitude awesome so here&#39;s some homework for you guys solve these questions and give me the answers in the comment section if you can take a scientific calculator to the exam feel free to use it for these calculations but if you&#39;re not allowed to carry a scientific calculator to the exam do use the basic addition and subtraction which i&#39;ve talked about so in india you&#39;re allowed to use a scientific calculator for the navigation exam but it&#39;s not the case in other countries and again i personally feel that everyone should know how to manually calculate these as well so this was all from my side guys hit me up if you have any doubts any suggestions and i&#39;m waiting for your answers in the comment section i&#39;ll see you next time thanks for watching

hello everyone welcome back in this video i&amp;#39;ll be talking about how to find the difference between two given latitudes or two given longitudes so this is also known as the change in longitude or the change in latitude now i&amp;#39;ll talk about everything that can be related to this topic i&amp;#39;ll start from the very basics of what is a latitude what is a longitude what is the equator what is the green which prime radian how do we measure longitudes how do we measure latitudes what is the reason why do we need to calculate the change in longitude of the change in latitude everything so if you want to know everything about latitudes and longitudes this should be the video for you i&amp;#39;m sure this is going to be helpful so let&amp;#39;s dive into it now before i start talking about what is change in longitude or what is the change in latitude i want to start with the basics so i want you to build your basics first so let&amp;#39;s start by how do we name latitudes and longitudes because if you understand this if your basics are strong you&amp;#39;ll be able to find the change in latitudes or change in longitudes very very easily i feel that that is just a very very small part of this video so let&amp;#39;s start with longitudes so what are longitudes longitudes are just vertical lines which are running from one pole to the other pole now in this diagram all the blue lines and the one red line are the longitudes okay now there&amp;#39;s a place called greenwich which is located in london it&amp;#39;s this place and the longitude which passes through greenwich which will be this longitude is called the greenwich prime meridian meridian is just another name for longitude so what is this greenwich prime meridian so this particular meridian is known as the datum meridian so what this means is that the meridians which are to the left or to the right of this greenwich prime meridian will be named according to the position or the angle they make with the greenwich prime meridian i&amp;#39;ll explain all this so what you need to know is that this meridian is the datum meridian right this is the main meridian now all the meridians which are to the west of the greenwich prime meridian are termed west and all the meridians to the east of the greenwich prime meridian are termed as east okay and since the greenwich prime meridian lies in the center it is known as zero degrees east slash west okay very easy so when i was talking about these meridians i said that the meridians are named according to the angle they make with the data meridian so what i mean is this so if you look at this diagram we can see that this is the greenwich prime meridian and there is a place b which lies on this medium yeah so this is actually the top down view of the earth so this is the north pole now i think it will be much more easier for you to visualize so this is the top down view of the earth the red line is the green ridge prime meridian and there&amp;#39;s a place b the longitude which passes through b is the green line now if we measure the angle between the greenwich prime meridian and the meridian that is passing through point b we&amp;#39;ll get this angle right let&amp;#39;s say this is 45 degrees angle so this meridian which was passing through point b will be the 45 degree east meridian why is this east because obviously it is to the east of the greenwich primary do you understand now i&amp;#39;ll take another example so let&amp;#39;s say there was a place c over here okay there was a place c and now if i make a longitude which is passing through c it will be something like this now the angle this makes with the greenwich prime meridian is 90 degrees so what we can say is that this longitude is 90 degree west longitude west because it is to the left of the greenwich prime meridian or it is to the west of the greenwich primary okay so this is the 90 degree west meridian if i talk about this this will probably be 130 degree west and if i keep continuing the maximum which i can get is this so the angle this meridian makes with the greenwich prime meridian will be 180 degrees so that meridian is the 180 degree meridian it is actually the anti-meridian of the greenwich primary what do you mean by anti-meridian anti-meridian is the meridian that is right behind the main meridian so if this was 0 degrees east west that will be 180 degree east west so that is the maximum value a longitude can have so the maximum value of a longitude is 180 degree east-west okay why is it east-west both because it is lying right between the east and the west meridians if i go over here this will be 90 degree east this will be 130 degrees this will be 140 150 160 170 and this main one will be 180 degree east or west because it is being shared between both the east and the west medians so these are longitudes i hope you understood the concept behind this now if we look at this view of the graticule we can see that this red line is the primary idiom now this line which is to the right will be probably 30 degree east since it&amp;#39;s to the east this will be 60 degrees this line which is to the left will be 30 degree west longitude this will be maybe 60 degree west and so on right so that is how we name or that is how we measure the longitudes so it is the angle the longitude makes with the prime meridian perfect now let&amp;#39;s look at what are latitudes so latitudes are parallel lines on either sides of the equator so all the blue lines and the one red line you can see are the parallels of latitudes so these are nothing but small circles so if you have watched the previous video you would know what are small circles and what are great circles so i told you there also that parallels of latitude are nothing but small circles so the equator is a great circle and small circles around the equator on either sides up to the poles are parallels of latitudes so the datum of these lines is the equator now the equator is known as zero degree north south latitude and any latitude above the equator is termed north and any latitude below the equator in the southern hemisphere are termed as south so this is the importance of the datum the datum decides what value has to be given to what latitude right now how do we measure these latitudes so if you look at this diagram now this is the straight on view of the earth so this is the equator and there is a place a on the surface of the earth so this point a lies on this latitude yeah so what we do is that we take a line from a which is a point on the earth we take that line to the center of the earth and we measure the angle it is making with the equator so this angle which is the angle between the equator and the line joining the place to the center of the earth is taken into consideration while naming the latitude so we can see that this angle is 40 degrees so what we can say is that this latitude is 40 degree north latitude why not because it is north of the equator and why 40 degrees because it is making 40 degrees with the equator right so now if i take a point b which is here so let&amp;#39;s say this is the latitude and the next thing we do is that we join this point to the center of the earth and we measure the angle between this line and the equator so it turns out that this angle is 60 degrees so this latitude will be 60 degrees south latitude okay now if i consider the poles so if i talk about the north pole if i draw a line from the north pole to the center of the earth i can see that this makes an angle of 90 degrees so the latitude at the north pole will be 90 degree not latitude and similarly the latitude on the south pole will be 90 degrees south latitude because it&amp;#39;s going to make 90 degree with the equator perfect so the maximum value a latitude can get is 90 degree north or 90 degrees south and the equator which is the datum is zero degrees not south latitude perfect now these latitudes and longitudes which we discussed so far are given in degrees like it was 90 degree note 60 degree south 40 degree north or if we look at the longitudes we talked about 60 degree east 60 degree west and so on but we can also get latitudes and longitudes in degrees minutes and seconds which can be something like this so we write it like this so this means minutes and this is seconds and obviously this sign is for degrees yep so since i&amp;#39;ve talked about minutes and seconds i want you guys to know about these very basic very small conversions so the first one is that one degree is equal to 60 minutes right and the second one is that one minute is equal to 60 seconds yeah very easy so i want you to keep these two conversions in mind so one degree equals 60 minutes and each minute equals 60 seconds it&amp;#39;s similar to what we use in time now how do we plot these points on the earth so if i am given this coordinate how do i plot it on the earth i&amp;#39;ll tell you it&amp;#39;s very easy so to plot this particular coordinate on a map i need two things to plot the latitude i need the equator which is the datum and to plot the longitude i need the prime meridian which is the datum for longitudes so let&amp;#39;s say this is the equator and this is the prime meridian now for 20 degrees north i&amp;#39;ll go 20 degrees towards the north from my equator so let&amp;#39;s say this was 5 degrees 10 degrees 15 degrees 20 degrees so this is my 20 degrees north latitude now from here i&amp;#39;ll go 45 degrees towards the east so this is 45 degrees towards the east from my prime meridian so prime meridian was this vertical yellow knight so now i&amp;#39;ll start going towards the right so this was 5 degrees east 10 degrees 15 20 25 30 35 40 45 so this is my 45 degree east latitude now this point over here will be the point that i&amp;#39;m looking for so this will be 20 degree north 45 degree east point so do you understand first i went 20 degrees up from the equator then i went 45 degrees towards the right which is towards the east from my prime medium and this point is what i was looking for so that is how we plot coordinates now if you understood whatever i have talked about till now believe me the other half of the video will just be a cakewalk for you i know a lot of you would already know whatever i&amp;#39;ve talked about right now but i want you guys to realize how important it is for you to know all this so now coming back to my initial question why do we need to find the difference between two latitudes or two longitudes why do we need to find the change in longitudes or the change in latitudes why so let&amp;#39;s say we are to find the distance between two places on the earth with these coordinates so the first place is 10 degrees not 30 degree west and the second place is 10 degree north 62 degrees east so the first thing i want to do is to plot these points to know where these points are so that is the equator prime meridian for the first point i&amp;#39;ll go 10 degrees north let&amp;#39;s say it&amp;#39;s here and 30 degrees west west is to the left so 30 degree west probably here so this is my point number one now the second point 10 degrees north which is again this point and 62 degrees east so now this will be to the right somewhere here so my point number two will be over here right now i want to find the distance between these two points so what i see is that both of these points are lying on the same latitude and this latitude is 10 degrees north the other thing that i can see is that the two longitudes are different so this point was on 30 degrees west longitude and the second point was on 62 degrees east longitude so if i want to find the distance between the two points obviously i need to find the distance between these two longitudes first and this distance between these two longitudes is known as the change in longitude so the reason we find change in longitude or the change in latitude is to find the distance between the two points right so here in this case we saw that both the points are on the same latitude the longitudes are different if someone wants me to calculate the distance between the two points i will definitely need to find the distance or the change of longitude that has taken place between these two points and that is where we find the change in longitude similarly if i look at this example now so here we have two points and if we are asked to find the distance between the two points the first thing that i&amp;#39;ll do is plot them so this is the primary median this is the equator so for the first point it is 51 degrees north somewhere here 12 degrees west so 12 degree west will be somewhere here so this is my first point and the second point is 6 degrees north somewhere here and 12 degrees west 12 degree west will be somewhere here so this is my point number two now in this example what i can see is that the longitude is same so both of these points are on 12 degrees north longitude the latitudes are different so the point number one was 51 degree north and the second point was at six degree north now if someone wants me to find the distance between point one and point two i will definitely need to know about the change of latitude that is taking place between the two points right first point was at six degree north and the second point was at 51 degrees north so i have to know that there is a difference of 45 degrees between both of these points only then i&amp;#39;ll be able to calculate the distance between them right so this is where change in longitude or change in latitude comes into play so this is change in latitude so now i hope you understood why we need to calculate the change in longitude or the change in latitudes perfect next i want to talk about basic addition and subtraction of degrees i don&amp;#39;t know how good you guys are at this already but it&amp;#39;s my duty to teach it so here it is so there are two latitudes given one and two and i want to add both of them so i&amp;#39;ll tell you how i do it the first step is to write everything separately first i&amp;#39;ll write the first latitude is 22 degrees 15 minutes and 25 seconds now below this i&amp;#39;ll write the second latitude which is 21 degrees 10 minutes and 35 seconds and i want to add these so this was the first step to write everything separately so that i can add degrees to degrees minutes to minutes seconds to seconds so the answer will be 60 seconds 25 minutes and 43 degrees right now what we can see from here is that 60 seconds can also be written as one minute right so what we do is we take one minute and add to the 25 minutes so it becomes 26 minutes and 43 degrees with zero seconds so this is the answer 43 degrees 26 minutes zero seconds so why zero seconds because we took the 60 seconds converted it to minutes and added 1 minute to the already 25 minutes we had so that is how we add two latitudes now similarly if i wanted to subtract 10 degrees 25 minutes 50 seconds from 40 degrees 15 minutes and 34 seconds what i do is write everything separately number one so it will be 40 degrees 15 minutes 34 seconds and below it 10 degrees 25 minutes 50 seconds i want to subtract perfect so this will be 30 degrees and oops 15 is smaller than 25 similarly 34 is smaller than 50. now what do i do so one thing at a time first we see that 15 minutes is smaller than 25 minutes so i cannot subtract 25 from 15 i&amp;#39;ll have to do something so what i do is that i take one degree convert it to minutes which will be 60 minutes and i put it over here so what happens is that this 40 becomes 39 degrees and i get 15 plus 60 which is equal to 75 minutes over here right now i see 75 is bigger than 25 so i can subtract 25 from 75 minutes next i see that 34 seconds is smaller than 50 seconds so what do i do i do something similar so i take one minute and convert it to 60 seconds right so this 75 becomes 74 minutes and this 34 becomes 34 plus 60 which is 94 seconds so if i look at it my new equation will be 39 degrees 74 minutes 94 seconds minus sign 10 degrees 25 minutes and 50 seconds so i can easily subtract now the answer will be 44 seconds 49 minutes so this will be my answer which is 29 degrees 49 minutes and 44 seconds so this is how we add and subtract latitudes and longitudes now good news for some people so if you are allowed to carry a scientific calculator all this is gonna be easy for you as you can directly put in degrees minutes and seconds to add or subtract in your scientific calculator now if i use a scientific calculator for this same example i won&amp;#39;t have to do anything i just put the values and i&amp;#39;ll get the answer so i&amp;#39;ll put 40 press this key which is for the degrees i&amp;#39;ll put 15 press this key again now it&amp;#39;s acting as the minute scheme and i&amp;#39;ll press 34 press this key again which is for the seconds now i&amp;#39;ll use the subtract function and put the next value which is 10 degrees 25 minutes and 50 seconds and if i look at the answer the answer is 29 degrees 49 minutes and 44 seconds so you see how easy it becomes with the scientific calculator yeah so if you&amp;#39;re allowed to use a scientific calculator feel free to use it but what i personally feel is that everyone should be able to calculate this manually because anyone can do it with a calculator right you should know how to do it manually just end of story perfect so now you know what are latitudes what are longitudes how do we measure latitudes how do we measure longitudes you know how to add how to subtract units in degrees minutes and seconds so perfect finding the change in latitudes or the change in longitudes will be very very easy for you now so now let&amp;#39;s look at how to find the change of latitude or the change in longitudes so in the exam there will be direct questions on just to find the change in longitude or the change in latitude number one next type of questions will be for you to find the distance between two given points and you&amp;#39;ll see that when you&amp;#39;re asked to find the shortest distance between two given points which is the departure you&amp;#39;ll obviously have to find the change in longitude so these are the two type of questions you can expect in the exams okay now when you&amp;#39;re asked to find the change in longitude or the change in latitude between two given lats or two given longs you&amp;#39;re supposed to give a value in degrees minutes and seconds of the shortest distance between the two given latitudes or longitudes so just keep this in mind that you have to find the shortest distance between those two latitudes or those two longitudes right perfect now let&amp;#39;s learn by examples so in the first example it asks us to find the sheila at between 55 degrees 29 minutes south to 31 degrees 48 minutes south so this is my equator prime meridian for the first point it says 55 degrees 29 minutes south so i go 55 degrees 29 minutes south which is somewhere here so this will be one latitude which is 55 degrees 29 south and the second latitude is 31 degrees 48 minutes south so it will be somewhere here it&amp;#39;s 31 degrees 48 and it&amp;#39;s south and this was the equator which is 0 degrees north south so what i have to find is the change between these two latitudes so the red area it&amp;#39;s very easy so you see this was 55 degrees something and this was 31 degrees something so now do you think that if i subtract 31 degrees 48 minutes from 55 degrees 29 minutes the thing i&amp;#39;ll be left with will be this part right and that is exactly what i have to find so what i&amp;#39;ll do is i&amp;#39;ll take 55 degrees 29 minutes and i&amp;#39;ll subtract 31 degrees 48 minutes from this so if i use my calculator i&amp;#39;ll put 55 degrees 29 minutes minus 31 degrees 48 minutes and the answer comes out to be 23 degrees 41 minutes right so this is the change in latitude now if i put the north south values in this so it was 55 degrees south and 31 degrees south now i want you to read the question again so in the question it asks what is the change in latitude between 55 degrees to 31 degrees right it said a value from this to this so that means that i&amp;#39;m moving from 55 degrees towards 31 degrees which means that i&amp;#39;m moving towards the north right 31 degrees is north of 55 degrees so i&amp;#39;ll put a value north over here now the value of change in latitude is complete so it is always complete when i give a direction so my change in latitude is 23 degrees 41 minutes north perfect now let&amp;#39;s look at another example so in this example it says that what is the change in latitude between 26 degrees 57 minutes south to 14 degrees 25 minutes north okay so the first thing here again is that we&amp;#39;ll plot these points so this is my prime meridian this is the equator which is zero degrees north slash south the first latitude is 26 degrees 57 minutes south so let&amp;#39;s say it&amp;#39;s somewhere here so this is 26 degrees 57 minutes south and the second latitude is 14 degrees 25 minutes north so it will be somewhere here north of the equator so this is 14 degrees 25 minutes north now i want to find the change in latitude between 26 degrees to 14 degrees so i want to find this value it&amp;#39;s very easy again so you see this was 26 degrees 57 minutes right and this was 14 degrees 25 minutes to find the red arrow i just add both of these i&amp;#39;ll put 26 degrees 57 minutes add 14 degrees 25 minutes to it what do i get i get 2 82 minutes and 40 degrees now obviously i cannot leave it in 82 minutes so it will be 41 degrees and 22 minutes right because the maximum value of a minute is 60. i cannot go above 60 minutes if i&amp;#39;m exceeding 60 minutes then i&amp;#39;ll have to subtract 60 from this and add 1 to the degrees right because 1 degree was 60 minutes perfect so it is 41 degrees and 22 minutes now for the north south value it was 26 to 14 that means i am going towards the north so i&amp;#39;ll put north and this is my change in latitude between 26 degrees 57 minutes south to 14 degrees 25 minutes north perfect so i hope you understood the point here now a small trick so if both the latitudes are in the same hemisphere we usually subtract one from another like in this diagram if we were talking about 30 degrees south and 60 degree south to find this area we&amp;#39;ll have to subtract 30 degrees from 60 degrees right similarly if i was talking in the northern hemisphere it was 30 degrees and let&amp;#39;s say this is 15 degrees so to find this change i&amp;#39;ll have to subtract 15 degrees from 30 degrees right that is what is written in this slide so it says north not subtract south south subtract which was this case and it says not south add so what this means is that if we were talking about two latitudes let&amp;#39;s say 15 degrees and 15 degrees now i want to find this region what will i do obviously i&amp;#39;ll add this 15 to this 15 and i&amp;#39;ll get 30 degrees so this will be my change in latitude so for north south we have to add so this is a very basic trick you can use to find the change in latitudes now let&amp;#39;s look at some change in longitude examples so the first example here asks us that what is the change in longitude between 82 degrees 35 minutes east to 132 degrees 42 minutes east so the first thing we do is plotting now to plot for change in longitudes there is a separate diagram so this is the earth this is the north pole this is the greenwich prime meridian which is zero degrees east west and this is its anti-meridian which is 180 degree east west so you remember this diagram from the beginning it&amp;#39;s the same now if i&amp;#39;m going towards the right it is east if i&amp;#39;m going towards the left it is west perfect so the first longitude is 82 degrees 35 minutes east so it will be this longitude 82 degrees 35 minutes east so if you remember we take the angle between the longitude and the prime reading and it should be equal to the name of the longitude so this angle would be probably 82 degrees right so the yellow one is the first longitude and the second longitude is 132 degrees 42 minutes east so it will somewhere be over here says 132 degrees 42 minutes east this is number two this angle also looks more like 132 degrees right so i&amp;#39;ve plotted both of the longitudes correctly now what i want to find is the change or the difference between these two so this was 132 this was 82 if i subtract 82 from 132 i will be left with this right so i&amp;#39;ll write 132 degrees 42 minutes east minus 82 degrees 35 minutes east zero seven minutes 50 degrees so the answer will be 50 degrees 7 minutes you know if i talk about whether it will be east or west so we go back to the question it says between 0 8 2 degrees and 1 3 2 degrees so that means we are going from this longitude to this longitude so we&amp;#39;ll just look at these arrows now so looking at these arrows we see that we&amp;#39;re going in the direction of east right so i&amp;#39;ll put east over here so this is my change in longitude between 82 degrees 35 minutes east and 132 degrees 42 minutes east this is also very straightforward very easy perfect now let&amp;#39;s look at the second example so it&amp;#39;s asking us what is the change in longitude between 0 0 4 degrees 32 minutes west to 0 1 0 degrees 15 minutes east now again i&amp;#39;ll draw the same diagram for change in longitude this is the earth north pole prime meridian anti-meridian this side is east and this side is west okay so the first longitude is four degrees 32 minutes west so it will be somewhere very close over here this will be zero zero 4 32 west and the other longitude is 10 degrees 15 minutes east so it will be on this side now 10 degrees 15 minutes east and what i have to find is this difference between the two longitudes now if you see that even this is the change in longitude right this is also a difference between the two why am i always finding this distance so the answer to this is because i want to find the shortest arc so this is the shortest arc so if i want to go from 4 degrees west to 10 degrees west obviously i&amp;#39;ll take this path right i won&amp;#39;t go all the way in this path right i want the shortest distance so that&amp;#39;s why i&amp;#39;m finding the shortest arc so how do i find this i see that this is 10 degrees 15 minutes east and this is 4 degrees 32 minutes west so i will add both of these up and get the required change in longitude so it will be 0 zero degrees 15 minutes east plus zero zero four degrees 32 minutes west the answer will be 47 minutes zero and four degrees and in the question it says that we are going from zero zero four to zero one zero so it would be zero zero four two zero one zero that means going in the eastward direction so i can put east over here and this is my change in longitude 14 degrees 47 minutes east perfect now the last example asks us to find the change in longitude between 140 degrees 27 minutes east to 160 degrees 54 minutes west so again we&amp;#39;ll make the earth the north pole prime meridian anti meridian the direction arrows and we plot the points so the first point is 140 degree east so since this is 180 degrees 140 will be somewhere here 140 degrees 27 minutes east and the next point is 160 degrees 54 minutes west so even this point will be close to the 180 degree east west line so let&amp;#39;s say it&amp;#39;s this so it is 160 degrees 54 minutes west perfect so now i want to find this difference i don&amp;#39;t want to find this difference because this is a longer arc i always look for the shortest arc so this one can be a bit tricky for you if you don&amp;#39;t pay attention so this was 180 degrees right that is the prime reading now this is 140 degrees and 27 minutes so if i want to find this much area can i subtract 140 from 180 will i get this red difference yeah i can so i&amp;#39;ll write 180 degrees minus 140 degrees 27 minutes and i&amp;#39;ll find this now similarly on the other side this was again 180 degrees yeah and this was 160 degrees 54 minutes so to find this area can i subtract 160 degrees 54 minutes from 180 degrees yeah i can get this red arc as well so for that i&amp;#39;ll write 180 degrees minus 160 degrees 54 minutes and i&amp;#39;ll find that and to find the total i&amp;#39;ll have to add both of these up so when i add both of these up what i&amp;#39;ll get is this value so what i did was i subtracted 140 from 180 i got this area and i subtracted 160 from 180 to get this area then i added both of these up to get the total area so this is my plan so for this i&amp;#39;ll use the calculator it&amp;#39;s much faster so i&amp;#39;ll take 180 degrees subtract 140 degrees 27 minutes from it i&amp;#39;ll get 39 degrees 33 minutes and get 39 degrees 33 minutes and for the next one it is 180 degrees minus 160 54. this comes out to be 19 degrees six minutes so after adding both of these up i&amp;#39;ll get 58 degrees 39 minutes so this is my change in longitude now in the question it says that i am going from 140 to 160 that means i am going from here to here so this will be the arrow and this arrow is again in the eastward direction so i&amp;#39;ll put east over here so the change in longitude between 140 degrees 27 minutes east and 160 degrees 54 minutes west is 58 degrees 39 minutes east right 160 degrees is east of 140 degrees because we&amp;#39;re going towards the right and that arrow is towards the east so perfect i think now you&amp;#39;ll be able to find the change in longitudes and latitudes very very easily just keep in mind that we always go for the shortest arc while finding the change in longitudes and don&amp;#39;t forget to draw this diagram so whenever you&amp;#39;re finding the change in longitudes or the change in latitudes always draw diagrams it helps you imagine what&amp;#39;s going on and whenever you draw the diagrams never forget these arrows because these arrows will help you understand this part of the answer and a change in longitude or a change in latitude is incomplete without a direction so always draw these arrows always draw the diagram and never forget to write the direction of the change in latitude or the change in longitude awesome so here&amp;#39;s some homework for you guys solve these questions and give me the answers in the comment section if you can take a scientific calculator to the exam feel free to use it for these calculations but if you&amp;#39;re not allowed to carry a scientific calculator to the exam do use the basic addition and subtraction which i&amp;#39;ve talked about so in india you&amp;#39;re allowed to use a scientific calculator for the navigation exam but it&amp;#39;s not the case in other countries and again i personally feel that everyone should know how to manually calculate these as well so this was all from my side guys hit me up if you have any doubts any suggestions and i&amp;#39;m waiting for your answers in the comment section i&amp;#39;ll see you next time thanks for watching

Transcript for:Calculating Latitude and Longitude Changes

Transcript for:
Calculating Latitude and Longitude Changes