Topographic Map Scale

Another thing you need to understand about a topographic
map is scale. Obviously, maps aren't life-sized. Otherwise
we'd never be able to fit them in our backpacks. Instead,
cartographers plot maps on a ratio scale, where one
measurement on the map equals another larger amount in
the real world.
The first number of the scale is always one. It's your unit
of measurement, usually an inch. The second number is
the ground distance. For example, if your U.S. Geological
Survey (USGS) map has a scale of 1:24,000, it means that
one inch on the map is equal to 24,000 inches (2000 feet
or 609.6 meters) in the real world. Your map's scale legend
will always be at the bottom.
For USGS topographic maps, 1:24,000 is the scale most
often used. Maps based on metric units use a scale of
1:25,000, where one centimeter equals 0.25 kilometers.
You'll find most of the United States mapped at the
1:24,000 scale, with only a few exceptions. Puerto Rico, for
example, maps at 1:20,000 or 1:30,000 because the
country originally mapped at a metric scale. A couple of
states map at 1:25,000, and most of Alaska (due to its
size) maps at 1:63,360. The more populated areas of
Alaska, though, map at the typical 1:24,000 or 1:25,000.
A 1:24,000 map is large and provides a lot of detail about
the area -- it will include buildings, campgrounds, ski lifts,
among other things. You may also see footbridges and
private roads on a map of this scale.
It requires about 57,000 maps at this scale to cover the 48
contiguous United States, Hawaii and territories [source:
USGS]. However, you can find maps of various areas at all
different scales. The scale corresponds to its intended use.
For example, township engineers generally need extremely
detailed maps that show sewers, power and water lines,
and streets. The common scale for these maps is 1:600. If
you want to see one large area on a single sheet but with
less detail, a smaller scale map like 1:250,000 is better.