Contours

Contour lines are used to represent three-dimensional shapes on flat surfaces. They are used on maps of various kinds to give the appearance of depth or perspective. Meteorologists use them to show air pressure, water vapor, and rainfall.

The most common form of contours are those used on topographic maps. Here contour lines connect continuous points of equal elevation.

Imagine yourself standing on a hillside. You would be able to determine whether you walked uphill or downhill. But suppose you wanted to walk AROUND the hill without walking either uphill or downhill.

In other words you want to walk a level path. That level path would be a contour.

Heres are some other ways to visualize and understand contours.

Look at these two pictures

Take a bowl, like a rice bowl or a soup bowl, rounded, cone shaped, whatever.

Put the stopper in the sink and put the bowl upside down in the sink.

Run a small amount of water until it is half an inch or so of the bottom of the bowl. Stop the water.

Look a where the water touches the bowl. The water level is a countour on the bowl. Flat water intersects protruding bowl. The 'shoreline' represents a contour on the bowl.

Run more water until the water level rises on half inch or so higher.

Now look at the 'shoreline'. This represents a higher contour line on the bowl.

Repeat this, adding half an inch or an inch, or even two inches of water at a time to the sink. Stop each time and look at that 'shoreline' on the bowl.

Now imagine all of those shorelines drawn on the bowl. They would form concentric circles (depending on the shape of the bowl), and would define the bowl's shape. The detail would depend on how much the depth of water changed each time.

On a map each contour is where the 'shoreline' would be if the land was flooded to that level.

Map contours are always the same vertical distance apart on a given map. This is called the 'countour interval', and represents the change in level of this imaginary water that would flood the land.

Now do you see why they say that a countour is the intersection of a flat plane with the landscape (topography)?

You would get the same shapes by slicing the landscape (or the bowls!) the way meat is sliced in the deli. The thickness of the "slices' is the contour interval.

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Here are some links that might help:

CUNY ©David J. Leveson

Understanding Topographic Maps

Topographic Movies

I'm looking for more links and will add them as they come.