Reading and Using Maps
What does the scale of a map tell me?
A scale indicates the level of detail and defines the distances between objects on a map. On a map, scales can be written as a fraction, a verbal description, or as a bar scale.
A fraction, or ratio, using the example of 1/100,000 or 1:100,000, indicates that one unit of any form of measurement on the map is equivalent to 100,000 units of the same measurement in the area being represented. For instance, if you use inches as the unit of measurement, then one inch on the map would equal 100,000 inches in the area represented by the map.
A verbal description describes the relationship as if it were a verbal instruction, such as “one inch equals one mile.” This allows the versatility of having different units of measurement.
A bar scale uses a graphic to show the relationship between distance on the map to distance in the area represented. The bar scale is the only type of scale that allows a reduction or enlargement of the map without distorting the scale. This is because when you increase the size of the map, the bar scale is increased proportionally. For a fraction or verbal scale, the proportion (1:1,000) is only true for the map at that size. For example, when enlarging a map, the map might become twice as large but the numbers in a ratio do not change, as they would need to in order to stay accurate.