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The easiest way to depict a point on a two dimensional map is with two lines
that cross. One line that goes up and down on the map and another that goes
side to side. Where they cross is the location of the point you are interested
in -- a waypoint, an island, or where you are at a given point in time. Those
working with charts refer to those lines as the coordinate lines. Usually they
are given as a set of numbers for one line and another set of numbers for the
second line. Placing the two lines on the chart indicates a point.
This is simple enough to understand. However, there are many different
coordinate systems in use. I have added some convertors here to address
the three most commonly encountered.
-
DMS (Degrees Minutes Seconds) - This is the most popular coordinate
system. Remember that there are 360 degrees, but you can only go up to 90
degrees north or south latitude, or just short of 180 degrees east or west
longitude. At the equator a degree of longitude is over 69 miles wide, so
smaller divisions are required for depicting points accurately. This system
is best remembered like what is used on a clock. Think of a degree as an
hour. Each degree is broken up into 60 minutes, each minute is broken up
into 60 seconds. A degree = 69.1722 miles, a minute = 1.1528 miles and a
second = 101.45 feet.
Example: 27° 37' 45" N, 82° 42' 10" W
-
DD.MM (Degree Decimal Minutes) - This coordinate system is becoming
more and more visible as it is becoming the standard many governments
have set between themselves for handling coordinate data. It also seems to
be used by at least some GPS receiver manufacturers for handling data
within their units.
Example: 27° 37.761 N, 82° 42.179 W
-
DD.DD (Decimal Degrees) - Decimal degrees simply refers to angular
measurements being expressed in decimal terms. For example, one and a half
degrees would be expressed as 1.5 degrees. Using the degrees, minutes,
and seconds notation, one and a half degrees would be expressed as 1 30'
00". These are simply two different ways of expressing the same value.
Decimal degree have a significant advantage over DMS, as you can calculate
with them much easier. For sailors, the DMS my be an advantage as one
minute corresponds (reasonably closely) to one nautical mile.
Example: 27.629273 N, 82.703053 W
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| Click here to use the Coordinate Convertors |
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