Topographic maps are useful because they help us understand and locate topographic features on Earth's surface. But in order to properly read a topographic map, you need to be able to interpret its lines, symbols, and shapes correctly.
Take a look around you. You can see that the earth is not one flat plane, right? It has hills, mountains, valleys, and other features that give its surface a 3-dimensional shape. These features create topography, which is simply the shape of Earth's surface. The way we represent these features is on a topographic map. Also called a contour map, this is a 2-dimensional representation of Earth's 3-dimensional surface. Like any map, a topographic map shows us where certain features are located. But instead of identifying city boundaries or the best route to work, this type of map identifies topographic features and their elevation either above or below sea level.
One of the first things you'll notice about a topographic map is the contour lines. These are elevation lines on the map in either feet or meters. Contour lines are farther apart in areas of lower elevation, but get closer together in areas of higher elevation. Think of it like this: if you looked down on a mountain from above, you would see the peak in the middle and the rest of the mountain spreading out around it. The areas nearer to the mountain peak look closer together because these areas are more vertical than they are horizontal. In other words, they have a steep slope, so from above, you see less of them. But as you get closer to the bottom where the elevation is lower, the ground spreads out in a more horizontal fashion so you see more of it from above. Looking at a topographic map is just like this, and the contour lines help you see the shape of the land through the elevation.
Contour lines may twist and turn with the landscape on the map, but they don't ever cross, and they don't ever split. Contour lines also turn to a 'V' or 'U' shape when they cross a running water body like a stream or river. Index contour lines have elevation values printed on them and are darker or thicker lines. These are the reference contours on the map, from which you can determine other elevation values. If every contour line had a printed value the map would get pretty messy. So instead, these contour lines show you elevation periodically with intermediate contour lines in between.
The space between contour lines is called the contour interval. Each map will have a different contour interval depending on the topography of that area. Areas that are fairly level do not need to show great changes in elevation so they may have smaller intervals, like maybe 10 feet. But if the map is showing an area with quick changes in elevation, 10-foot intervals would make for a lot of contour lines on the map, so it may be more appropriate to show contour lines for changes every 100 feet instead.
Scales and Other Features
All maps have a horizontal scale, which tells you the ratio of a map distance to the actual distance on the ground. Topographic maps are no exception, but they also have something special: a vertical scale. This incorporates the vertical dimension of the map, which is necessary because we're dealing with 3-D features.
Topographic maps also have other reference features, including roads, buildings, vegetation, and water bodies like lakes, rivers, and streams. These are important because they, too, are a part of the landscape and are relevant to the topographic features.
And of course, just like any map, a topographic map will also have a key. The key contains all of the information about what each symbol, shape, line, and color means on the map. This may change from map to map, since some maps will have certain features that others do not.
Maps come in all different types and they help us understand what's around us. A topographic map is no exception, providing us with a 2-dimensional representation of Earth's 3-dimensional surface.
These maps are often called contour maps because of their contour lines. These are elevation lines on the map in either feet or meters, which are closer together in areas of high elevation and farther apart in areas of low elevation. The distance between contour lines is called the contour interval, which can be determined by comparing the the contour lines with elevation marked on them, known as index contours.
Topographic maps show us Earth's topography, but these features are much more meaningful when we know what else is around them. Therefore, topographic maps also show features such as buildings, roads, water bodies, and vegetation, which gives topographic features context and relevance.
You could accomplish the following subsequent to completing this lesson:
- Indicate the purpose of topographic maps
- Identify contour lines, contour intervals and index contours
- Recognize other features of topographic maps