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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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posted:3/4/2012
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