Topographic maps use contour lines to show elevation and surface shape. Index contours are labeled with increasing numbers, with lighter lines in between representing smaller increments. Contour intervals allow for numerical elevation determination. Contour lines can be measured in different units. They also show surface definition, such as the shape of an island or mountain.
Topography is a field that explores the surface of the earth. Finds are often documented on topographic maps. Such maps usually contain many lines, known as contour lines. These are used to reveal the shape of the surface and to indicate the elevation of various areas.
It may be easier to understand contour lines if you access their functions individually. One function of these markings is to show how high or low the surface is at a particular location. This is usually referred to as elevation.
Sea level is the point at which the surface of the water and the surface of the land are equal. The elevation of this point is zero. Contour lines are generally comparable to sea level. These markers will show how much higher or lower than sea level an area is.
The space between each contour line is known as the contour interval. This is what allows a person to determine elevation in numerical terms. On a topographical map, a person should see that some lines are darker than others. Variable tones denote varying contour ranges.
The darker lines are called index contours. Instead of trying to label each row with a number, which could result in a jumbled and confusing diagram, only certain rows are labeled. The number representing each outline of the index should increase in equal increments. Therefore, if the first contour of the index is 10, the next must be 20.
Between two contour lines of the index finger, a person should find four lines that are lighter in color. Each of these will also have equally increasing increments but not as large as those represented by the index outlines. The contour interval of these lighter lines should equally represent the space between the two index contours. If the first outline of the index is 10 and the other is 20, the four lines in between should represent 12, 14, 16 and 18.
Arranging contour lines in this way provides greater accuracy. It also prevents a person from having to do too many calculations. A person must check each map because contour lines can be represented by various measurements, such as feet, miles, or meters.
The second function of contour lines is surface definition. These lines show what an area looks like. Some maps use an overhead view, which shows what the terrain should look like if a person is up looking down. For example, if an island were a perfect square, contour lines would reveal that. If, however, there was a perfectly circular mountain on that island, that too would be shown.
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