| Background: The Properties of a Map | |
| All maps must contain three basic elements to be useful: | |
| |
 Locations should provide two pieces of information. These are the portion of the Earth's surface covered by the map and a means of locating any point within the map area. The first is generally
done with an insert image showing the map position relative to some larger feature,
Earth, continent, etc. What it is relative to depends on the size of the region covered by the map. A map must show direction so that one can use it to orient oneself with a
compass, measured relative to geographic north. Unfortunately, a compass points to magnetic north not true north. This
point is defined by
the Earth's magnetic
field. Magnetic
declination is the difference between the two norths and should be indicated on a map. It varies with position on Earth (both
in direction, e.g.,
east or west, and magnitude). It also varies with time. Distance indicates how large an area of
the Earth's surface
a map covers, done by using a scale. Three different types of scales are used. Verbal scale is described
by words, e.g., one
inch equals a mile. It
is convenient but lacks
precision. A graphical or bar scale uses a bar to denote a certain distance on the ground. It is more accurate. The bar can be divided into fractions of
measurement units. The
most accurate type of
scale representation is
a proportional scale. Indicated by a ratio or proportion, e.g., 1:10,000. This scale indicates that
one unit on the map equals 10,000 units on
the ground. This
works very well for metric systems but is somewhat confusing with the English system of
measurements. 1:63,360 is one inch to one mile. Sometimes this is
simplified to 1:62,500, which is slightly less than an inch to a mile. | |
| |
| |
Copyright Houghton Mifflin Company. All
Rights Reserved. | |
