Geology Topographic Maps

What’s the difference between topographic (contour) maps and regular maps? Regular maps show where places are. They also give directions. Contour or topographic maps tell the elevation and shape of the land.

A contour map (cont.) Uses contour lines to show different elevations.

Contour lines Show points on the earth that have equal elevation above sea level.

Contour intervals The difference in elevation between successive contour lines.

Cartographers Are Map makers Arthur H. Robinson created a pseudocylindrical map of the globe.

Some contour lines have marked elevations. These markings tell us elevations in feet usually in the U.S.

Many contour lines don’t have marked elevations.

We can determine the elevation of the unmarked lines 1st note the number of lines between marked elevations. Include the second marked line but not the one you started with. 2nd Find the difference between the first and second marked line. 3rd divide the difference by the number of lines found between the marked lines. your answer is the contour interval.

Unmarked lines (Continued) Once you determine the contour interval you simple add the interval to the first marked line to get the next line.

The rule of “V” What happens to contour lines when it crosses a river? The contour lines form a “V”.

Why do they form “V”s? They form “V”s to let us know which direction the river is flowing. The “V” always point Up stream. Rivers flow in the opposite direction of the point of the “V”

Why do they form “V”s?

Gradient Gradient tells how steep an area is. We express gradient by stating the average gradient between two points. Usually shown by stating the average difference in elevation divided by the horizontal distance.

Example

Gradient on a topographic Shown by how close together the lines are. If the lines are farther apart the hill is less steep. If the lines are close together the hill is more steep. http://academic.brooklyn.cuny.edu/geology/leveson/core/linksa/contourspacing.html

More on contour lines Contour lines cannot cross because each line shows a different elevation. Contour Lines Can Never Intersect Because A Point On The Surface Of Earth Cannot Be At Two Different Elevations.