Two Projected Coordinate Systems: UTM and State Plane
A coordinate system called Universal Transverse Mercator14 was developed based on a series of 60 projections onto semi-cylinders that contact the Earth along meridians. (To consider, for example, one of these projections, imagine a sheet of paper curved so that it becomes a half cylinder whose radius is that of the Earth’s. Then, with the axis of the cylinder oriented in an east–west direction—hence the term transverse—the paper is brought into contact with a globe along the meridian designating 3° longitude. Then, the surface of the Earth between 0° and 6° is projected onto the paper). This process is repeated for central meridians of 9°, 15°, 21°, and so forth up to 357°. The term “zone” is ambiguously used for this swath of territory. However, UTM projections are further subdivided into areas, also called zones, covering 6° of longitude and, for most zones, 8° of latitude. Further, ArcGIS divides a total zone into a northern and a southern part. In any event, a coordinate system is imposed on the resulting projection such that the numbers in any given zone:
- Are always positive
- Always increase from left to right (west to east)
- Always increase from bottom to top (south to north)
The representation of our previously discussed object (at 38° N and 84.5° W) in the UTM coordinate system, when that system is based on WGS84, is a “northing” of 4,208764.4636 meters and an “easting” of 719,510.3358 meters. The northing is the distance ...