Okay, so now we're going to look at doing a cross-section. To do a cross-section we're visualising what the shape of the land would be just straight from our topographic map. So if we have a look at this topographic map, which is of Perisher Valley, is the vicinity of Little Thredboe River.
Now, we could do a cross-section from Pendley Gap over to Bull Creek and we would be looking at how each of these contour lines, we would represent each of these contour lines onto our topographic cross section. Now that's what you need. to do as part of one of your exercises.
I'm not going to do it now because it would just take forever and it's not great using a big thick pen. So I've simplified it by using a pre-made diagram, like so. So here we have a simplified diagram showing some contour lines. So here we have a spot height of 476 metres. We've read off the map that the contour interval is 10 metres and we've got one other contour line marked with its elevation.
So just double checking that so it's 476. We're obviously going down the hill that would be 470, that would be 460, 450, 440. This one over here would be 430 because we know it goes down. We're looking at the whole landscape and double checking as we go along. long, they could go up again like this one.
470, 460, now that's 450, that must be 460, so we've got a bit of a flat area between two hills. Alright, so just make sure you understand your elevations and what each of the contour lines mean. It can get quite difficult, especially in mountainous areas, you need to be very careful. Okay, to do a cross-section you take another piece of piece of paper, any piece of paper with a flat edge. We're going to do our cross section from point A to point B over there.
We take our piece of paper, just makes it thankfully, and Wherever we intersect a contour line, we put a mark on our piece of paper. There's a mark there, a mark there, a mark there, a mark there, one there, one there, one there, one there and one there. We then need to make sure we know which of those contour lines are represented by those marks. So this one over here is 440, this one here is 450, you know that's 460, that's the same one so that's 460. we're going up that's 470 that's the same one that's 470 and we're coming down 60 50 460 450 and 440 okay so once we have done done that we can get rid of our map and we take another piece of paper or ideally what you would want to have is graph paper that works really well but we'll do our own graph This is just easier to see.
So we take our X axis along there and we make a Y axis. Now the scale along the along the bottom is going to be the scale of our map, which in this case, just made it up, but let's say it's 1 to 25,000. So that would be one centimetre equals what?
25,000 centimetres. Or one centimetre equals 250 metres, which is fine. That's the scale we're going to use as we go along across the landscape. But if we use the same scale for our y-axis as one centimetre equaling 250 metres, so we have one centimetre there.
Now if we said that was meters, the range of elevations of our topographic map only go from 470 to 440. So we would have a very flat representation of the elevation and wouldn't really show us ...very much. So we need to exaggerate the vertical scale. Now you can pick the vertical scale of whatever you like, trial and error, to try and get the best representation of the of the topography on your diagram.
Now I think you're asked to do a couple of different vertical exaggerations in the exercises but really what you should be doing if you're doing this to really see the elevations to try and work out which one suits your topography best perhaps a shallower one a smaller one where it's very hilly and a bigger one if it's flatter, just to exaggerate the topography. I'm going to use a vertical exaggeration of, I'm going to pick one, let's say a vertical exaggeration of 5. So it needs to be 5 times bigger, the vertical scale, than the horizontal scale. So if our horizontal scale is 1 to 25,000, what would be 5 times bigger?
Not 25,000 times 5. Remember? remember right back, you do it the other way, because you want a larger scale. So you would divide 25,000 by five, so it's one to 5,000, okay? So your vertical scale would be one to 5,000, that's a larger scale, and you've exaggerated it.
So in that case, with a vertical scale of one to 5,000, then that's one centimeter equals 50 meters. And that should work relatively well. Is it going to work well? One centimetre equals 50 metres. Let's have a look.
Let's mark on the map our scale. 2, 3, 4, 5, 6, 9, 10. So then this would be 50. 100, 200, 300, 400 and 500. And to plot our cross section, oops, it's not quite long enough, make sure you don't fall into that trap. You then plot on your topographic cross-section the elevation at each of your tick marks.
So here we have 440, so that would be there. Then we have 450, okay, at that tick mark. You can use a ruler. This is where graph paper comes in handy. Okay, so 450 is about there.
Move that along there. 460, just doing it by eye for the sake of speed. 460, then... 460, it's not quite right is it? Anyway, 470, 470, should have used graph paper, 460 and 450 and then we would draw a line to show our cross-section and quite honestly that's not a very good topographic cross-section because our vertical exaggeration wasn't chosen well.
To get that, to be able to see much more of the topography you would have to examine the topography. exaggerate that vertical scale even more. And I'll let you do that with your topographic map.
I think you get the idea of what's required. I don't need to do that again. All right, so vertical exaggeration is important to get that right. Okay.