A contour line is a (usually brown) line on a map joining points of equal
altitude (height above mean sea level).
The contour interval is the distance vertically between the altitude each individual contour line represents. When
reading a map, contour lines give you information on what the topography of the area is likely to be. The closer the contours
the steeper the ground. By interpreting contour lines it is possible to imagine a 3 dimensional picture of what the ground
might look like.
Some 1:50,000 scale maps of the Rocky Mountains have a contour interval of 100 feet; i.e. separate contour lines are drawn
joining points of altitude 4000, 4100, 4200, 4300 etc feet above mean sea level. 1:250,000 maps of the area have a contour
interval of 500 feet. Using a 100 foot interval on these maps of the Rockies would make them too cluttered. There are some
1:50,000 scale maps of the Rockies that have a 20 meter contour interval below 2000 meters and a 40 meter interval above 2000
meters - these can be very confusing. Others have a 50 meter contour interval. So it is important to check the contour interval
on every map! However in Saskatchewan some 1:50,000 scale maps have a contour interval of 10 feet and 1:250,000 scale maps
have a contour interval of 100 feet. This is necessary to show any variation of altitude there. In the mountainous areas of
the US, contour intervals seem to be 80 feet on the 1:62500 scale maps and 40 feet on the 1:40680 scale and 200 feet on the
Understanding Contour LinesAt first glance all the wiggly brown lines on a map may seem meaningless but detailed
study of them can reveal a lot about the landscape. With practice, from studying contour lines you will be able to form a
3-dimensional picture in your mind of what an area may look like.
What about other shapes of contours that represent ridges and valleys? Which are the ridges and which are
the valleys? The analysis is often made easier by there being a blue line representing a stream, and streams usually run in
valleys. A good way to find out where the ridges and valleys are is to Draw a Section:
- The closer the contour lines the steeper the ground.
- Closed contour lines represent mountains or hills.
- Closed contour lines with dashes represent depressions or hollows.
One must realize that this is an approximation of the terrain. The following illustrates two equally valid interpretations
With continued study of topographic maps and contour lines you will be able to picture your hike from the map while sitting
in your armchair. However that must not stop you getting out there and doing it!!