SCALE


Scale tells the size relationship between the map or model and the real earth. It can be written in three ways, the verbal scale, the graphic scale, and the representative fraction (RF) or fractional scale.

The verbal scale is a simple statement of the scale such as one inch equals one mile or 1" = 1 mile. The unit on the map should be appropriate to the dimensions of the map. One of what ever unit should be given to eliminate the need for further conversion. The distance on the earth should be as easily comprehendible as possible. The purpose of the verbal scale should be the clearest and fastest communication of the size relationship.

The graphic scale is a divided line on the map with the line lengths designated as to the equivalent distance on the real earth. Several different graphic scales are usually given on a map so that different units of measurement may be applied. Note that the 0 is often NOT on the left edge but rather a small portion of the scale with finer subdivisions than to the right. The graphic scale is the most useful scale if the map will be reproduced and changed in size, because both the map and the graphic scale will change in the same ratio while the other scales will no longer be valid. To use the graphic scale, mark the distance between points on the edge of a sheet of paper. Then put the right hand mark on an evenly measured mark to the right of the zero SUCH THAT the left hand mark falls between the zero and the left edge of the scale. Read off the whole units on the right and the fractional units on the left. If the length is more than one graphic scale long, be sure to consider the position of the zero in adding the lengths measured off. If a non-linear length is being measured, measure progressive linear segments along the edge of a sheet of paper and use the graphic scale in the same manner. Thus, if a graphic scale is given, do NOT use a ruler to measure the distance on the map; it is much more difficult to obtain accurate results.

The representative fraction (RF or fractional scale) is a ratio between the distance on the map and the distance on the real earth. Three basic rules apply. First, the numerator of the fraction is always ONE. Second, both numbers represent the SAME UNIT OF MEASUREMENT. Third, NO UNIT of measurement is ever given with the representative fraction. The representative fraction is the best scale if the map is not to be reproduced and changed in size because it does not rely on any particular measurement system (British, Metric). What ever unit of measurement is represented by the numerator, the denominator represent the exact same unit of measurement. Representative fractions can be written in three different styles. Example: 1:63,360 or 1/63,360 or
__1___
63,360.


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