Now the fourth kind of scale that you will see on maps is a bar scale, also called a graphic scale. That is a... bar with one or more divisions within it, labeled to tell you how long it is. So that distance, whatever that be on the map, represents one mile on the ground.
On the US Geological Survey Long Beach map, right under the ratio scale of 1 to 24,000, there are in fact three bar scales. The first one here in miles is an unbroken mile over here and a second mile broken down into fractions on this side. The second one, feet, a total of eight thousand feet, seven thousand coming this way, one thousand going that way. from the zero line and the third one kilometers a whole kilometer here and a second kilometer broken into tenths over there by the way this information here is often known as the representative fraction of the map the bar scale is particularly useful in our modern computer environment. The maps I've been showing you, you can't use any of these number scales because the actual scale of the map depends on the size of your screen and the zoom you applied.
It varies a lot and all that happens to a scale like 1 to 24,000 is that the numbers get bigger or smaller as you zoom. But the bar scale... If you enlarge the map, you enlarge the scale with it. If you shrink the map, you shrink the scale. The bar scale always tells you the right answer.
If you look at like Google Maps or any of these computerized applications, the bar scale is all they put on. They're not going to attempt to calculate numerical scales for you. They just present the bar scale which is automatically however you decide to display or print or copy and paste the information.
We classify map scales into small scale, medium scale and large scale. Using the common US Geological Survey map scales, the large scale map is our 1 to 24,000 scale like we use on the Long Beach map. Medium scale, 1 to 62,500.
By the way, again, let's try to... Make that scale easier to understand. One inch. How many inches are there in a mile?
There are 63,360 inches in a mile. So one inch, approximately one mile. This one was one inch, approximately two fifths of a mile. One inch, one mile.
That's a typical small scale map. 1 to 250,000, 1 to 1 quarter million, 1 inch is about 4 miles. Now this may seem backwards. Large, you see a smaller number here. Small, we have a larger number.
But realize that... this is like a fraction and if we put it back as a fraction one over G, the 24,000 is on the bottom and 1 over 24,000 is definitely bigger than 1 over quarter million. Okay, so that's how the apparent contradiction between the small, medium, and large and the large, medium, small numbers large, medium, small denominators. Here is a comparison of those three map scales.
On the left the small scale one to quarter million, middle, medium scale, one to 62,500 or one inch approximately a mile, and on the right the large scale, one to 24,000, one inch equals two thousand feet or about two fifths of a mile, the same as the Long Beach map that we've been using. These three sample maps centre on a small town called Gorham, somewhere back east, and let's see what we can get. from each of the maps. The small scale map. You see the area, you see all the major highways, you see that Gorham is a small town with basically a crossroads.
You can travel through it on the north-south direction, you can travel through it in a more or less east-west direction, but you don't know anything about the town itself, it's just a small pink blob. But what roads to take to go if in different directions go to other places, very useful. Moving up to the medium scale map, one inch to a mile approximately.
Now the pink blob has expanded substantially and you learn that that crossroads in town it's not that simple. You can travel straight through the town on this approximately north-south route but if you come in from the west you can't just go straight through you actually have to jog over a block. Those roads don't.
are not continuous. Couldn't see that on here, wasn't room to show it. Now we can show that.
Okay, you can see the roads leading out of town, where they go to. Well, you have to figure that one out. That isn't apparent on this map. Then as we move to the large-scale map, even more detail becomes apparent. Here the urbanised area is just a pink blob.
Here every street large and small is shown and the individual houses along the sides of the streets are shown. Are the individual houses shown the actual size and shape that they are? No, it doesn't go to that amount of detail. If you look at this carefully you'll see there are two shapes, square and elongate rectangle, and all they've done is to add whichever one fitted the best. You might ask, this is the same scale as the Long Beach map they've been looking at.
Why don't we show individual houses in Long Beach? Well, this is a small semi-rural community and the houses are reasonably spaced out. If we tried to jam in every house in Long Beach, it would, I'm afraid, become an almost solid black mass.
It wouldn't be usable. And so that's why they continued in the densely packed urban environment of Long Beach to go on just using the pink tint for the urbanized area. Now larger buildings, notice the high school and the state teachers college here, larger buildings are shown the actual size and shape they are and that is also true on the Long Beach map where when you look back at it you'll see that schools, churches, civic buildings, things like that are buildings of the college. are all marked in the exact the actual size and shape that they truly are.
Okay, so the small scale map is good for an overview of the area. You get a reasonable amount of real estate onto the map but lacking detail. Medium scale map. Improves on detail but reduces the area that you can see and the large scale map is the most extreme in that regard.
Plenty of detail but only a very small area shown. So here you get to compare the scales for the three different maps. You've got a bar scale and a ratio scale for each one.
When would you use a bar scale versus a ratio scale? Well for quick eyeballing The bar scale, definitely the best. Let's ask the question, how far is it from the high school to the state teacher's college?
Well, eyeballing it, you just want a quick comparison of distance. Let's see, that's the distance, that's about that distance, it's about half a mile. Quick, easy, not very accurate. If, on the other hand, let's say you're in charge of a project, you're going to install high-speed internet cable between the two places.
It's extremely expensive. You don't want to buy too much. What are you going to do? You are going to measure the distance along the route that you take very accurately using a ruler to, you know, a 32nd of an inch or a fraction of a millimeter, whatever units you decide to use. as accurately as you possibly can.
And once you have measured the distance on the map, you will multiply by 24,000 to find that distance in real life. And that will be way more accurate than guessing what fraction of this last unit here was it when we eyeballed the distance on the bar scale. So both kinds of scales have their uses. Next thing that we want on every map, number five if you will, direction.
Where is north? Well it's at the top you say. Often true, not always. Think of a road atlas. Every state fits on a page.
By the way, that means the scales differ wildly from one page to another. If Connecticut fits a page, you can drive across the page in an hour or two. If Texas fits on a page, it takes you a day to drive across that page. But since not all states are page-shaped, sometimes they'll be on their side.
North will be down. If you have and can easily identify latitude and longitude lines, lines, or point north. But usually a map has on it what we call a north arrow, often a rather fancy decorative affair, pointing north, but sometimes kind of subdued to be less obvious.
There's a town in North Wales called Llandudna. It's a beach resort, has been since Victorian times. The way the town makes money is people come to spend their summers going to the beach.
Now, when you get up to... England, Wales, Scotland. You're further from the equator than we are here. It's pretty chilly. And people want warm beaches.
And you know, south-facing beaches get more sun. So south-facing, south coast always seems like the right place to go. Llandudno's beach faces due north. Which you can realize if you look carefully at the people's shadows.
So what do the good folk in the Chamber of Commerce do? they printed the town plan, the street layout, upside down so that the north-facing beach is at the bottom because if it's at the bottom of the map it must be facing south and they put the north arrow on rather small and facing down. Yeah, it's a deliberate deliberate attempt at deception but they didn't actually falsify it.
The information is there if you look. What does the North Arrow look like on the US Geological Survey map of Long Beach? Well, it's neither large nor decorative, but here it is. What's the significance of the star at the top, do you think? Well, it's Polaris, the North Star, so that's the line that points to true north.
In the next video, I'm going to ask the question, on the ground, how do you find north?