Data Hacking

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FIGURE 8-2: Lines of longitude
Chapter 8 — GPS Data
You can take a measurement of latitude and longitude (although the convention is to use longitude
followed by latitude) and combine them to get a fixed point of the Earth’s surface. This is
similar to the grid system used in games such as Battleship in which by specifying how many
squares to move along and up, you get to the square in question.
For example, 0° longitude, 0° latitude (written as 0°, 0° ) is a point in the Atlantic Ocean off the
coast of Africa, while 180° east (or west, for that matter) longitude, 0° latitude is still on the
equator, but this time on the other side of the world completely, in the Pacific Ocean, off the
coast of Fiji.
Degrees are a good start to plotting coordinates, but they aren’t as precise as possible. What you
now need to do is further divide the degrees into minutes. Each degree consists of 60 minutes:
12° 12’ N 04° 08’ W
N
In addition to minutes, you can add even greater precision by adding decimal parts of a minute:
12° 12.255’ N 04° 08.345’ W
Instead of using decimal minutes, you can also subdivide minutes into seconds (where one
minute has 60 seconds). However, decimal minutes are the general coordinate format used with
the WGS84 datum system that we are going to use here, and they are the default units shown
on GPS receivers.
No matter what coordinate format you choose, the actual location represented on the planet is
the same. The numbers may be different, but the location is the same. For example, the following
three sets of coordinates represent the same spot on the globe:
N 38 deg 26 min 48.517 sec, W 76 deg 5 min 38.192 sec
N 38 deg 26.80862 min, W 76 deg 5.63653 min
-76.0939423, 38.4468104
S
Greenwich Meridian
E
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