Every map is smaller than the portion of the earth it represents. Scale is the proportion of the map to the actual area shown on it; e.g. ½-inch (on the map) equals 50 miles. It states the area and distance relationships if measurements are necessary.
Scale is shown by a line segment divided into certain units of lengths (a graphic scale). The presence of a scale allows the user to determine the extent of the mapped area. When scale is expressed as a ratio (with the first term always being 1), it is called a representative fraction. This ratio was first used in France in 1806 and was quickly adopted as a sort of ‘international language’.
Since all maps distort – and the distortion might vary from one part of the map to another – a scale will give only an approximation. But on larger scale maps, which include only a small portion of the earth, the distortion may be negligible and the scale more accurate.