Topographical Maps

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Topographical Maps

• What are they?
• How do you read one?
• Why are they useful?

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Topography

• Refers to the human and physical surface features
  of an area
• Topo maps have contour lines that show elevation

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Draw its profile
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Draw its profile
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Rules for Reading and Creating

• Mean sea level is an elevation of 0 feet
• Every point on a contour line has the same
  elevation above sea level
• Always check the map or state specifically the
  contour interval in use

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• Contour lines never cross one another

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• Contour lines are closed figures

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• Small, closed loops indicate hilltops
• Ridges are hills that are long and narrow

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• Spacing of contours depicts slope

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• Where streams are shown on a map, the contours
  always form a V or a U shape with the apex
  pointing upstream (higher)

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• Hatchure Lines represent a depression. They point
  in to the lower elevation.

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• Elevations indicated precisely are spot
  elevations or benchmarks. Spot elevations have
  been checked by surveyors. Benchmarks are exact
  elevations inscribed on a brass plate in the
  ground.

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What are these features?
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• Slope (Brown)
• The steeper the slope, the closer the contours,
  because it takes less distance to rise or fall a
  given amount on a steep slope.
• Hill (Yellow)
• Contours are concentric with maximum elevations
  in the center
• Valley (Blue)
• Lower elevations in the center. Contours form V's
  that point upstream.
• Ridge (Green)
• An elongate hill. Elevations high in the center.
  Contours form V's pointing downhill.
• Depression (Red)
• Uncommon, and usually shown with hachured
  contours. The hachures are on the downhill side.
• Saddle (Purple)
• The landform that confuses more beginners than
  any other. Land slopes downhill in some
  directions, uphill in others. Any time you have
  four elevation points, with the points on one
  diagonal high and the other low, you probably
  have a saddle.