Topographic Maps

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Topographic Maps
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What is a Topographic Map?

• Topographic maps are special maps that show the
  relief (highs and lows) of Earths surface.
• Topographic maps are different from regular maps
  because they use isolines in addition to
  everything else.

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What is an Isoline?

• Isolines are lines that connect equal values.
• The values are different depending on the map
  being used.
• Types of Isolines
• Isotherms connect equal points of temperature
• Isobars connect equal points of air pressure
• Contour lines connect equal points of elevation

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Contour Lines

• For topographic maps, contour lines are the type
  of isoline used to show equal points of
  elevation.
• They look like the background of this powerpoint
  presentation!
• Contour lines show three different things on
  topographic maps
• Elevation of the land
• Shape of the land
• Steepness of the slopes

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Contour Lines

• Contour lines look like this

• All the points on the 200 line equal 200 meters,
  all along the 300 equal 300 meters, etc.
• We know the elevation is in meters because it
  tells us at the bottom of the map.
• By using contour lines, we can take a real-life,
  3-dimensional hill and draw it on a flat,
  2-dimensional map!!!

Elevations in meters
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Topo Map Link
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Reading Contour Lines

• The contour interval is the amount between each
  line.
• The contour interval in this map is 100 meters
  since each line goes up by 100.

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Reading Contour Lines

• Usually, not every line is labeled for you. It
  will either tell you the contour interval at the
  bottom of the map, or you will have to figure it
  out.

50
100
150
300
250
200
Contour Interval 100 m
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Reading Contour Lines

• The closer the contour lines are to each other,
  the steeper the hill.
• The further away the contour lines are from each
  other the more gentle the hill.

GENTLE!!
STEEP!!
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Reading Contour Lines

• Each line goes UP by the contour interval unless
  it is a hatchured contour. Those indicate
  depressions (holes).
• The first hatchured contour after a regular is
  the SAME value as the one that came before it,
  then each one after that goes DOWN by the contour
  interval.
• Then the first regular contour after a hatchured
  is the same as the hatchured before it and then
  they go UP by the contour interval after that.

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Estimating Elevations

• If a point is right on a contour line, you
  definitely know its elevation. But, if its
  in-between 2 contour lines, you must estimate.

B
We know for sure point B is 200 m because its
right on the 200 m contour line.
We dont know point As elevation for sure though.
Its probably about 350 m
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Other Contour Line Rules

• Contour lines NEVER cross each other!
• Contour lines NEVER split!
• Contour lines MUST begin and end at the edge of
  the mapcannot start or end them in the middle of
  the map.

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Drawing Contour Lines

• You must ALWAYS connect points of equal value!!
  Kind of like connect the dots when you were
  little!
• The lines you draw should be gentle, curving
  lines, no sharp angles or edges.

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• CORRECT!!!

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NOT CORRECT!!!
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Gradient

• Gradient is the average slope of a particular
  area on a map.
• You can calculate gradient for any map that has
  isolines.
• Formula Change in field value
• Distance
• Formula is on page 1 of ESRT!!!

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Gradient

• The field value is whatever the map is measuring.
• If its a topo map, its elevation.
• If its a weather map its probably air pressure
  (isobars) or temperature (isotherms).
• The distance is just the distance found between
  the 2 points given using the map scale.

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Example
Gradient change in field value Distance
B
Gradient 350 m 200 m
2.3 miles
Gradient 150 m 2.3 miles
Gradient 65.2 meters/mile
0
1
2 miles
Elevation in meters
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