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Explain II Script: Reading Topographic Maps and Satellite Images

We’ve already learned that a topographic map is a special kind of map. It takes the three- dimensional information from the world around us and puts it in a flat drawing. Topographic maps show natural structures like mountains, valleys, and lakes but they also show man-made structures such as roads, boundary lines, radio towers and major buildings. Topographic maps are used by engineers as they look for coal, oil and gas. They can be used to plan residentially and commercially. They are also used by the military and for recreational purposes like hiking and camping.

Also to review, when you look at a topographic map, those lines that you see that tell us about the features of the world are called contour lines. The relationship between topographic features and contour lines are shown here in this picture. So you have a top view which is the flat two-dimensional view you would see on the map and below is the three-dimensional view of the landforms and the shape of the earth that we would see if we went outside. So, it’s taking the 3-D view and making it flat and two-dimensional. Contour lines are the lines that are showing the elevation.

A contour interval is the change in elevation from one line to the next. What is the change as you go up each line? Imagine each line like a step up or a step down. So as you can see in the drawing, it’s showing you the three-dimensional model if you were looking at it from the side and how we are taking it and making it one flat map that you would look at from a top view. Each line represents a line of elevation as you look at that mountain.

Notice how the contour lines are used to show how gentle or steep the slope is. Again, depending on how close or far apart they are, you can tell whether this landform is going to have a steep or gentle slope. The closer the lines are, the steeper the slope is. The further apart the lines are, the more gentle the slope. You can see in the drawing- steep slope means it’s harder to climb and it’s more of a straight up and down slope. A more gentle slope would be easier to climb, and it’s more spread out.

Again, remember what a depression can show on a contour map. The contour lines have those little teeth marks on them called hachure marks and those indicate that the elevation is decreasing rather than increasing. It means that you might have a depression or a sinkhole or a crater that’s going downward into the ground rather than up out of the ground.

When we start to talk about satellite images today, remember that satellite images are digital pictures taken from satellites. We know that topographic maps are showing the 3-D features of the land on a flat map. They are tied together because both of these things help scientists keep track of changes in the Earth’s surface. Over time, the Earth’s surface does not stay the same. It’s always changing. Changes to the Earth’s surface may be short of long periods of time. The changes that cause what we see could be caused by a catastrophic event, ecological succession, erosion, weathering, and deposition.

This is a picture of what we might see in real life, at the top, and how the land has a shape and has elevation and at the bottom is the matching topographic map. If you look at the shapes up here and see we have some gentle, rolling peaks, and here we have this tiny little bit of land that comes out into the water. You can see the same shape below in the topographic map, except the topographic map has lines that are indicating elevation. Here you can see we have a steep slope, which we can see up here in the picture and a gentler slope over here on this side that is shown here by this hill. We have a little inlet of water and a stream which you can also see in the picture. Look at the coastlines, and look at the landforms that you have and try your best to match them together.

Here’s another view. You have the real life side view and you have a satellite view- remember that a satellite view is a view taken from way up in space. These are the pyramids in Egypt. The left picture is the pyramids from the top. The right picture is the pyramids from the side. We call the one on the left a satellite view because it’s a picture taken from space by a satellite that shows a landform, looking down at it from the top.

These slides coming up are all different views of the same landform, so you’ll have a satellite view on the left and a side view on the right. Don’t forget that a satellite view is a view taken from space. This one is the Grand Canyon. Notice the satellite view is the view from above- you can see the river snaking through, and we have the steep sides, and then the side view is what you would see if you were actually there. You can see the river there it’s just that it doesn’t look the same as the satellite view. You can still tell the two pictures were taken in the same place.

Here we have a satellite and side view of a meteor crater in Arizona.

The satellite and side view of the Mississippi River.

And of Mount Saint Helens. The satellite view you can tell, you can see some steep sides, you can see a little bit of a crater or a depression in the center. On the side view you can clearly see that- you can see the smoke coming out from the volcano so you can look and compare the two pictures and see that they are different views of the same thing.

In Nepal we have a national park; we have a satellite view and side view. You can see the mountain range again from above you can see that there are very steep sides and a long chain of peaks and then you see the same thing in a side view.

What we’re going to do now is practice looking at landforms and topographic maps and answering some questions. The first question is asking, what is the elevation of Point A? Take a look at your map. Look at Point A, and take a look at your contour line. You should figure out by looking that Point A sits right on the 0 ft contour line. Here’s the zero and if you follow it around- since all points on this line have an elevation of 0 ft, the elevation of point A is zero. Anywhere you went on this line, would be zero. The whole contour line is all connected, so it’s all going to be the same elevation.

Next question- What is the elevation of Point B? Again, if you are observing your contour lines and you see where B is and you follow the contour line all the way around, you should be able to answer: 10 feet. Point B sits right on the 10 ft contour line.  Since all points on this line have an elevation of 10 ft, the elevation of point B is 10 ft.

What is the elevation of Point C? This is a little trickier, if you take a look. Point C does not fall on a line. Observe what you see around it, and the answer is: Point C does not sit directly on a contour line so we cannot determine the elevation precisely.  We do know that point C is between the 10ft and 20 ft contour lines so its elevation must be greater than 10 ft and less than 20 ft.  Because point C is midway between these contour lines we can estimate the elevation is between 11 and 19 feet. It can’t be 10, because it’s not touching the 10. It can’t be 20, because it’s not touching the 20. Since it’s between, it has to be between 11 and 19 feet.

What is the elevation of Point D? Again, take a look very carefully and look at where Point D is. Think about what that answer might be. For Point D, it’s the same thing. Point D is not touching a line- I know it’s very close but it’s not, it’s actually inside. Since it’s inside the 20 foot contour line it’s indicating its elevation is above 20 ft. Its elevation has to be less than 30 ft. because there is no 30 ft. contour line shown.  But how much less? There is no way to tell. The elevation could be 21 ft, or it could be 29 ft. Just like we did with Point C.

Next, taking a look at this map the first question asks, Name the highest elevation shown for this volcano. What you need to do is observe very carefully everything you see on the map- all of the contour lines, and try to find the top of the volcano. If you’re looking at the very top point of the volcano you should see that the highest elevation is 2500. 2500 is the highest point. Question number 2 is asking, what is the contour interval of this map? Contour interval is how much every line is worth. How much is it increasing? Take a look at your contour lines. We have a line that says 1000, a line that says 1250, a line that says 1500, and then it keeps going – 1750, 2000, 2250, and 2500. You need to do a little math and ask, how much is it increasing every time? The answer is 250. The contour interval is 250.

Satellite images- we’ve already looked at some, we’ve looked at some side by side, but this is going to be a little bit different. Look at the images on the next slides. Match each image to the correct topographic map. Use the shape and elevation of the land to help you. Your job is to match the correct topographic map with the satellite image that it goes with.

Take a look. You have three topographic maps across the top and you have three images across the bottom. What you need to do is match the topographic maps with one of these images below. Which one goes with each? Which one looks like it matches with the other? The answers will be on the next slide. Look carefully at the shapes. The other thing that’s always a clue is water – it’s always a big clue. If there’s water, look for water in the topographic map. If it has steep sides, look for the contour lines that indicate steep sides. Your answers should look like this.

So, this one is kind of a giveaway because it has all that water that pools at the top, so it matches to this one right here. This one you can see has steep sides and what looks like an empty space in the middle, which could be a crater, which matches to this one right here. This one you see lots and lots of contour lines that on the side indicating climbing elevation on all sides and getting very steep near the top. That would be this one over here.

Finally, we have matching the topographic map on the left with the side view of the landform on the right. Which one do you think matches? You need to match each one. Look carefully at the shape, look at how many peaks it has, is it a gentle or a steep slope? These are good questions to ask yourself when you have to match things together.

Here’s what you should have for a solution. You have four topographic maps on the left are matched with its landform on the right. You can see the one on the left is match with the landform on the lower right because it has one peak with one steep side and one gentle side. The next one you can see has two peaks, so it matches to the landform side view over here that has two peaks that are pretty much even in elevation. The third topographic map matches the one right here because it only has one peak and pretty much a gradual slope all the way around. Last, this topographic map has two peaks which match to this landform here that also has two peaks but you can see that the elevation is very different between the two peaks. One has a gradual, almost flat slope and the other one has more elevation and more contour lines showing that it’s taller than the other.

Finally, here are a few review questions you might want to think about. If you can answer these, you know your topographic maps! Write these down in your science notebook, or you might want to discuss them. Number 1 is how are contour lines drawn on maps? Meaning, why do they look the way they look? Number 2 how does a contour map show whether a slope is gentle or steep? Number 3 describe at least four natural or man-made structures that can be shown on a topographic map.

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