What is a coordinate system and why is it so important? Why is my school map showing up somewhere in the Gulf of Mexico?
Ever have this happen? You bring in a map of your state, try to overlay your city map and they just don’t match up? Maybe your map view comes up looking something like this one. This should be Here.
If your data is not overlaying properly, its most likely due to data that is stored in two different coordinate systems. So back to our first question, what is a coordinate system? If you have had a class in Algebra or Geometry, this figure to the right will look familiar.
Not all coordinate systems are alike Not all coordinate systems are alike. The two most common coordinate systems used by EAST students are the Universal Transverse Mercator (UTM) and the Geographic coordinate systems.
Longitude is the X coordinate. Latitude is the Y coordinate. Prime Meridian Prime Meridian Equator Equator The intersection of the Prime Meridian and the Equator form the axes of the geographic coordinate system. Equator: X Prime Meridian: Y (+x, +y) (East, North) (+x, -y) (East, South) (-x, -y) (West, North) (-x, +y) “Flatten out” the axes and the coordinate plane is like the one to the right. Longitude is the X coordinate. Latitude is the Y coordinate.
Geographic coordinates may be written in one of the following ways: Degrees, Minutes, and Seconds (DMS) Example Little Rock, Arkansas X = Longitude: 92 degrees W 45’ 33” Y = Latitude: 34 degrees N 32’ 52” Decimal Degrees: Example X = -92.2579 Y = 34.834 Equator: X Prime Meridian: Y (+x, +y) (East, North) (+x, -y) (East, South) (-x, -y) (West, North) (-x, +y)
The UTM coordinate system uses a “flat earth,” model and is divided up into the zones as shown below. The X axis is the Equator, and there is a different Y axis for each zone.
This map illustrates the UTM zone 15 North This map illustrates the UTM zone 15 North. The UTM coordinate system uses only one quadrant. Rather than using degrees, minutes, and seconds to measure distance from the axes, the UTM system is measured in Meters. The UTM coordinates Little Rock, Arkansas are: X= 559,713.08 Meters East Y= 3,843,632.12 Meters North
Even though the following sets of coordinate pairs represent the same geographic location, notice how different the numbers are. X = -92.2579 Y = 34.834 X= 559,713.08 Meters East Y= 3,843,632.12 Meters North If you tried to place features stored in two different coordinate systems in the same map you might end up with something like this. Little Rock