Components of maps
Despite their variety, all maps have similar components, or parts. These include
a title; a legend or key; a direction indicator; and a scale.
The title of a map identifies what the map is about and what parts of the earth it
shows. The title of some maps includes a date. Dates are useful on maps showing
features that change over time. A map with the title "Distribution of Population in
France: 1920", for example, should not be used when looking for figures on the
present population of France.
A legend or key explains the meaning of colors and symbols used on a map. A
map with areas shown in green, red, and blue might be misunderstood unless the
user knows what the green, red, and blue represent. The legend also explains the
meaning of symbols used on a map, such as stars for capital cities.
Every map should have a direction indicator. One such indicator is an arrow that
points north. A different way to find directions on a map is to study the parallels and
meridians. East and west directions follow parallels, or lines of latitude. North and south
directions follow meridians, or lines of longitude. Parallels and meridians cross each
other to form an imaginary grid over the earth. Because each degree can be broken into
60 minutes (') and each minute can be broken into 60 seconds ("), this grid can be used
to fix the precise location of any point on the earth's surface.
The most important longitude is called the Greenwich Meridian, because it passes
through a place called Greenwich in London where there is a famous observatory. The
longitude of the Greenwich Meridian is 0 degrees. At Greenwich local time is called
Greenwich Mean Time (GMT). All places on the same meridian have the same local
time. When it is noon at a given meridian, it is after noon or post meridiem (p.m.) at
places which lie to the east of it. This is because the earth rotates from west to east.
At the same time the sun will be before noon or ante meridiem (a.m.) at places lying to
the west.
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