Cartographic Representation - A Primer of GIS: Fundamental Geographic and Cartographic Concepts - page 194

Some map scale examples and sizes covered by USGS map sheets.
Images from http://erg.usgs.gov/isb/pubs/factsheets/fs01502.html
scale of 1:25,000. The maps at this scale are almost always metric, which
means that distance on the map and on the ground is measured using
meters or a unit of measurement related to the meter. A word expression of
scale of these maps is “one centimeter on the map equals 250 meters on the
ground.” Another word expression for this scale is “four centimeters equals
one kilometer.” In fact, for ease of reference, these maps were often called
“four centimeter” maps. But the words are still long. Every time the map
would be described, people would need to remember the phrase. If people
weren't familiar with the phrase, a great deal of explanation would be
needed. If we express the scale as 1:25,000, it's much easier. This means that
Some scale representations.