The Art of Topographic Mapping Chapter 2: Maps as Models of the Earth

This is what a topographic map looks like!

What is a Topographic Map? A topographic map or contour map shows the differences in the elevation of the land. Topographic maps show the three -dimensional ups and downs of the terrain on a two - dimensional surface. Topographic maps show natural features like rivers, lakes, and mountains. It also shows features made by humans like cities, roads, and bridges.

The USGS ( The United States Geological Survey is a government agency that makes topo maps for the entire United States. Its headquarters are in Reston, VA. The USGS also provides lots of info on volcanoes, earthquakes, rocks, and minerals as well.

Keys to Reading Topo Maps The first thing you need to know is what a contour line is…it is a line connecting points of equal elevation. All the points on that line are at the same elevation. The space between contour lines is the contour interval. Typically, this is 20 ft. The spacing of contour lines indicates the slope of the land. If they are close together, the slope is STEEP, and if they are far apart, the slope is GENTLE. Contour lines that have the elevation marked on them are called index contours. Steep Gentle Interval = 5 feet

A River Runs Through It When contour lines encounter a river or stream, they bend to form the shape of a “ V ”. The “ V ” points toward the area of higher elevation upstream. Therefore, the river or stream flows in the opposite direction the “ V ” points.

Up the Hill We Go! Contour lines form closed circles around the tops of hills and mountains. Contour lines also form closed circles around depressions, but they are marked with short, straight lines inside the circle. These are called hachures. Green arrows point to hachured contours

“X” Marks the Spot Most mountains are marked with a spot elevation, or a benchmark. Two different ways you will see this: X 1234 or BM 1234