# Geology

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```					  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.)
 Usescontour lines to show
different elevations.
Contour lines
 Show  points on the earth that
have equal elevation above sea
level.
Contour intervals
 Thedifference 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
1.   1st note the number of lines between
marked elevations. Include the second
marked line but not the one you started
with.
2.   2nd Find the difference between the first
and second marked line.
3.   3rd divide the difference by the number
of lines found between the marked lines.
4.    your answer is the contour interval.
Unmarked lines (Continued)
1. Onceyou 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/g
eology/leveson/core/linksa/contoursp
acing.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.

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