
Data Standards  Map Scale
Scale refers to the relationship or ratio between
a distance on a map and the distance on the earth it represents.
Maps should display accurate distances and locations, and should
be in a convenient and usable size. To accomplish this, maps need
to show information proportionately smaller than the realworld
objects they represent. This proportion is referred to as a map
scale, or the relationship between distances on the map and distances
in the real world.
Map scales are generally expressed
in one of three formats:
 representative fraction
 graphical scale
 verbalstyle scale
1:100 000
or
1/100 000
Figure
5: Representative Fraction or Ratio

In a representative fraction or ratio, the number
to the left of the colon (the denominator) represents a distance
on the map, and the larger number to the right (the numerator) represents
the actual distance on the earth's surface [See Figure 5]. The units
of distance are not included because they are the same on the map
and in the realworld, regardless of what they may be (ex. inches,
centimeters). The advantage of a representative fraction or ratio
is that any unit of measurement can be used (Monmonier, 1988).

Figure
6: Graphical scale

On a graphical or barscale, the length of the
scale represents a certain length of the earth. The units of measurement
are provided. In this example, metric and English units are both
given [See Figure 6]. The advantage of a bar scale on a map is that
it can be easily enlarged or reduced without affecting the accuracy
of the scale, assuming the reproduction is enlarged or reduced by
the same factor in both horizontal and vertical directions (Monmonier,
1988).
Verbal scales are a simple translation to a usable
unit of measurement, and can be as simple as "1 inch on the
map is equal to 2000 feet on the ground." This type of scale
is rarely used on maps, yet many maps are designed in such a way
that one commonly used unit on the map will equate to another commonly
used or easily estimated unit on the ground (Monmonier, 1988).
Large scale vs. Small scale
Given a map scale ratio or fraction, the larger
the second number, the smaller the scale (or less detail in the
map) [See Figure 7 and Table 3]. A map of 1:50,000 is of larger
scale than a map of scale 1:1,000,000. In other words, a map which
has a larger scale will represent features on the map larger. When
choosing a map scale, one must sacrifice the amount of area covered
in order to obtain greater detail.


Large Scale

Small Scale

Figure 7: Illustration of different map
scales

Table 3: Representative distances
for map scales:
Scale:

1 inch on map represents:

1 centimeter on map represents:

1:24,000

2,000 feet

240 meters

1:50,000

4,166 feet

500 meters

1:63,360

1 mile

633.6 meters

1:100,000

1.6 miles

1 kilometer

1:250,000

4 miles

2.5 kilometers

1:500,000

8 miles

5 kilometers

1:1,000,000

16 miles

10 kilometers

(SIC 2002)
A GIS does not use a specific scale per se, because
its maps can be enlarged, reduced, and plotted at many different
scales other than the scale of the original data. However, all maps
need to be converted to the same scale in order to be layered.
