How to Use a Map

Page 5

 

Contour

In order to determine the elevation of a regular contour line, or any particular spot on the map, you must know whether you are moving uphill or downhill from an Index Contour Line. Remember that contour lines not only indicate elevation, but also the shape of the terrain. You can use a couple of "rules of thumb" concerning the shape of contour lines and elevation.

  1. "U's" made by contour lines point downhill.

  2. "V's" made by contour lines point uphill.

Let's look at a couple of examples. 

 

 Contour Lines A7.jpg (143934 bytes)      Contour Lines A6.jpg (141020 bytes)

Click to Enlarge Pictures

 

Other indicators are:

  1. Terrain moves uphill from the right and left of rivers and streams.
  2. Any direction from a hilltop is low ground. (We will get into identification of terrain features later)

Changes in elevation are generally referred to as slope. Slopes can be gradual, steep, concave, or convex.

A gradual slope is shown on a map by contour lines spaced wide and even. The wider the spacing the more gradual the slope.

 

Contour Lines A8.jpg (34703 bytes)

Click to Enlarge Picture 

A steep slope has contour lines close together and evenly spaced. The closer the spacing, the steeper the slope.

 

Contour Lines A9.jpg (30153 bytes)

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A concave slope begins on high ground with a steep slope (close contour lines) and gradually ends with a gradual slope (wide contour lines). 

 

Contour Lines A10.jpg (54493 bytes)

Click to Enlarge Picture

A convex slope begins on high ground with a gradual slope and turns into a steep slope.

 

Contour Lines A11.jpg (51784 bytes)

Click to Enlarge Picture

These general classifications of slope can be used on virtually any terrain to determine how hard movement will be, and also for terrain association.

 

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