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Introduction to Topographic Maps

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Introduction to Topographic Maps Topographic Maps Two dimensional model of the Earth s surface (represents 3-D world) Topographic maps are also known as contour maps. – PowerPoint PPT presentation

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Title: Introduction to Topographic Maps


1
Introduction to Topographic Maps
2
Topographic Maps
  • Two dimensional model of the Earths surface
    (represents 3-D world)
  • Topographic maps are also known as contour maps.
  • Show elevation above sea level using contour
    lines.

3
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4
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5
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6
Real World
Contour Map
7
Topographic Maps
  • Contour Line
  • - line on a map that connects points of EQUAL
    elevation.
  • - show elevation and shape of the land
  • Relief Difference between high and low
    elevations

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9
Topographic Maps
  • Contour Interval
  • difference in elevation between each line. MUST
    be equal spacing.
  • Contour interval
  • 20 feet

580
560
540
520
10
Topographic Maps
  • Index Contour
  • Usually every 5th line is printed darker and has
    an elevation printed on it.

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12
Rules for Contours
  1. Contour lines never cross

13
Rules for Contours
  • 2. Contours form closed loops (even if not shown
    of the map.

14
Rules for Contours
  • 3. Contours bend upstream (uphill) when crossing
    a stream.

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16
Rules for Contours
  • The maximum possible elevation for a hill is 1
    less than what the next contour should be.
  • The highest possible elevation of the hill is
    just below the value of  the next line that is
    not shown

90
80
70
60
50
17
399
179
239
18
Closely Spaced Contours
  • Steeper Slope (Gradient) contour lines are
    closer together.

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Wide Spaced Contours
  • Gradual/Gentle Slope (Gradient) contour lines
    are farther apart.

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22
A
B
23
Depressions
  • Contour lines which show a depression, crater, or
    sinkhole on a map.
  • Shown by dashed lines (hachure marks) on the
    inside of a contour line
  • The elevation of the first depression contour is
    the same as the lowest regular contour near it.

24
Rules for Contours
  • The lowest possible elevation for a depression
    is 1 more than what the next contour should
    be.
  • The lowest possible elevation of a depression is
    just above the value of  the next line that is
    not shown

90
90
51
80
70
60
50
25
100
100
50
26
Benchmarks
  • a location whose exact elevation is known and is
    noted on a brass or aluminum plate.
  • bench marks are shown on maps by an X with the
    letters BM written next to them.

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28
Map Scales
  • Indicates the distance on the map compared to
    distance in the real world
  • Graphical - by a line divided into equal parts
    and marked in units of length.

29
Map Scales
  • Numerically usually by writing a fraction to
    show what part of the true distances map
    distances really are.
  • 163,360
  • One inch on the map equals 63,360 Inches in the
    real world.
  • (There are 63,360 inches in a mile)

30
Gradient
  • The slope between any two points on a hill
  • Gradient

Change in Field Value Distance
31
Gradient
  • A trail is four miles long as measured by the
    scale on a map. The beginning of the trail is at
    the 1,060 ft contour line and the end of the
    trail is at the 960 ft contour line. Calculate
    the gradient of the trail.
  • Gradient

1060 ft 960 ft 4 miles
25.0 ft/mi
32
Gradient
Contour Interval 20 ft
200
0
2
4
6
8
10
miles
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