Contours

Contour Lines on a Map Indicating Elevation

Many Scouts have initial difficultly understanding the concepts behind contour lines on maps.

Once you grasp how they work its usually quite easy to visualize what they are showing you.

Every point on a contour line is at the same elevation or altitude. So if you were to walk directly along a contour line on a map you would be staying at the same level neither rising or falling - even though you might be walking along the side of a hill. Look at the map below and also the 3 dimensional contour model representation at the bottom.

Here is an example of a USGS map with contour lines:

As a work of the United States Government, the image is in the public
domain. For more information, see the USGS copyright policy.

Below is an example of a contour plane 3D model that shows a physical representation of a contour lines, Architects and landscape designers use these models to plan major project landscaping work.

Of course in real life the terrain is usually smoothed between the contour levels but this gives a very good impression of how contours on maps translate to physical properties. Each of these layers just like a contour is the same vertical interval.

Some Contour Guidelines:

Intervals:
All the contour intervals on a map are consistent elevation differences per contour line, the contour interval amount (in feet for USGS) is marked in the maps legend. The USGS shows every 5th contour line bolded and marked periodically with an actual elevation in feet.

V-Shapes:
V shaped contours usually indicate valleys often with a stream or runoff wash at the bottom running though the point of the V which points upstream. They can also indicate ridgelines (if without any water features) where the point of the V head downhill - look for water features related to the overall slope or contour interval markers to be sure.

O-Shapes:
Closed circles or 'O' shapes in contours, especially approximately concentric ones, are normally uphill on the inside and downhill on the outside. Often significant highpoints will be individually marked with a peak elevation - look for these and tell tale marked terrain names (e.g. Hill, Mountain, Peak, Plateau)

The smallest 'O' shape is usually the highest area. It is possible the same configuration indicates a depression - so look for contour interval markers and other signs.

Spacing:
Where contours are very closely spaced this indicates a steeper slope than where they are further apart. If contours merge into a single line this indicates a cliff formation.

ACM 1/2007

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