What is the definition of scale? Scale is the relationship that the depicted feature on map has to its actual size in the real word (more: map scale).
All maps are modeled representations of the real world and therefore the features are reduced in size when mapped.
In other words, scale is the measurement of the amount of reduction a mapped feature has to its actual counterpart on the ground.
Graphic Map Scale
Graphic scales, also know as bar scales, as indicated by the name, show the scale graphically. As the name suggest, this type of map scale is a graphic format.
Some maps will have bars to denote the map units, other graphic map scales will have tick marks to show units.
Some graphic map scales will show both metric and imperial/customary units for reference like the map bar scale below.
Verbal Scale On A Map
A verbal scale is text based, with the scale shown as a number and type of unit measurement equal to a specified unit measurement on the ground. The left side of the verbal is the unit of measurement on the map and the right side of the ratio is the unit measurement on the ground.
For example the verbal scale, 1cm = 100 km means that one cm measured the the map represented 100 km on the Earth. This type of scale is sometimes confused with Representative Fraction scales.
REPRESENTATIVE FRACTION AS A SCALE ON A MAP
Like verbal scale, representative fraction (RF) scale is also a text based scale but no units are shown.
For representative fraction, or ratio scale, scale is a simple ratio of map to ground measurement. Representative fraction is written with numbers on both sides of the colon. The number to the left of colon is the paper, or map, units and the number to the right of the colon is those same units in the real world.
For example, a RF scale of 1 : 1,200 means that every one unit on the map is equal to 1,200 units on the ground. There is no notation of the actual unit type used on a RF scale.
Therefore a RF scale of 1:1,200 is the same scale as a verbal scale of 1″ = 100′.
USGS topographic maps typically have both bar scales and representative fractions (RF). The scale bars on this map from the U.S. Census shows multiple types of map scales.
