Geography Reference
In-Depth Information
Chapter 9
Projections and
Coordinate Systems
If the world were flat, it would be a lot easier—at least on mapmakers.
Unfortunately, that's not the case, so we're faced with the age-old prob-
lem of depicting features on a spheroid (that's the earth) on a flat piece
of paper (or screen).
To solve this problem over the years, people have come up with the con-
cept of map projections. The key thing to remember about projections is
that none of them is perfect. You simply can't represent the entire earth
(or even a small part of it) on a flat surface without some distortion.
The amount of distortion varies with the projection. Many projections
are quite good when used for a small or regional area. If you try to use
the same projection for a larger area, the distortion increases.
Let's look at the main problems with squashing the earth onto a piece of
paper. It's impossible for a projection to maintain an accurate portrayal
of area, distance, shape, and direction all at once. For this reason, you'll
find that some projections are more suited for your use than others.
For example, if we're interested in measuring the areas of lakes we've
digitized, we want a projection that is equal-area. This means that for
any given location on the map, the measured area will be correct. If
we are interested in measuring distances, we obviously need an equi-
distant projection.
In choosing a map projection, we need to decide whether our focus
is on shape, direction, area, or distance. Once we know that, we can
choose an appropriate projection. Of course, sometimes you don't get
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