CC3 measures coordinates and distances with a user-definable system called Units. Feet, inches, and meters are common examples of units, but you can create your own, like miles, microns, or parsecs.
Think of your drawing as a life-size model. For example, if you design a bridge, you might tell CC3 that each unit is equal to one foot before starting your drawing. For a city plan you might set each unit equal to a city block. Each time you plot the drawing, CC3 reproduces your design at whatever scale you choose for that plot.
CC3’s overland mapping templates are arranged so that one inch equals a mile - while it would be possible to arrange to have true-sized maps, this degree of precision is unwieldy. DD3 and other add-ons use Feet by default.
When you create a new template, determining your drawing units should be one of your steps. By default, one unit is equal to one inch. You can set a different value with the UNITS command (File Menu >Drawing Properties > Units). If you commonly use different units in your drawings, you may find it helpful to use drawing TEMPLATES.