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# Topography

Topography shows or describes the physical features or landforms of an area of land. These features can include mountains, hills, lakes, rivers, valleys, and oceans. Topographic maps can also record the elevation of an area. That is, how high it is.

A 3D topographic map.

## Topographic Maps and Contour Lines

Topographic maps show the physical features of an area by using contour lines. They can also show where mountains, hills, lakes, rivers, valleys, and the depths of the ocean are. Some topographical maps can even represent cities, roads, or dams. Contour lines are lines on a topographic map used to show changes in the height of the land. If the contour lines are very close together, the area of land is steep. When the lines are more spread apart, they show areas of land that are more level, or flat. A plain is an example of a flatter area of land.

A 2D map. The lines, called contour lines, are close together where the slope of a hill is steeper.

A 3D map. It’s what you would get if you raised the contour lines in the picture above.

## Geographic Depressions

Geographic depressions are areas of land that are lower than the areas around them. They can even be below sea level. These develop because of erosion over time, earthquakes, or an impact on the ground such as a meteor crater. Volcanic eruptions can also cause these geographic depressions because they can change the shape of the land around them. Some examples of geographic depressions are the Great Basin, Crater Lake, or Death Valley in Nevada.

A crater on the moon. Topography is relevant everywhere, even out in space!

## How do we make Topographical maps?

There are two main methods we use today to make these maps: direct survey and indirect survey. A direct survey is when a person on the ground, called a topographer, takes measurements with surveying equipment. He is looking for the exact location and elevation of the area.

A photo of a topographer.

This is usually used for what we can see and reach, like mountains and hills. We use an indirect survey for remote or inaccessible areas, or places that we can’t reach. Indirect surveys are done with satellite images, radar, and images taken from an airplane or helicopter. Isn’t that cool?

## Other Great Resources:

Topography – Wikipedia: https://en.wikipedia.org/wiki/Topography
What is Topography? – Mocomi: http://mocomi.com/what-is-topography/