Program in GIS

GEOG 5121 Project 1:
Coordinates and Projections

Brenton White

 

Projections
Mercator
Equidistant Cylindrical
Polar Stereographic
Lambert Azimuthal
Azimuthal Equidistant
Orthographic

GEOG 5121 Home Page

Mercator Projection

Figure 1. Loveland located on global map.

Figure 2. Loveland using coordinates for the State of Colorado.

Briefly (1-2 sentences) describe the geographic coordinate system in your own words.

The Geographic coordinate system specifies locations on the surface of the Earth by establishing a grid of longitude and a latitude. The prime meridian (longitude) is designated as 0 degrees and measurements of longitude are determined by the number of degrees east or west.  The equator establishes 0 degrees latitude and measurement of latitude is determined by the number of degrees north or south.

Briefly (1-2 sentences) describe the UTM coordinate system in your own words. Explain what "NAD83" means, how it differs from "NAD27."

The Universal Transverse Mercator (UTM) coordinate system divides the Earth's surface into a flat grid specified by zone numbers (01 through 60, east to west, each 6 degrees wide) and zone designators (C through X, south to north).  Each zone has a central meridian from which coordinates are expressed as northings (meters north of the equator) and eastings (east of the zone's central meridian).  False northings and eastings for each zone are used to avoid negative numbers, it has a maximum error or 1 in 2,500 (1:2500), and this coordinate system does not cover the areas near the poles.

NAD83 stands for North American Datum of 1983 and is the basis upon which measurements (x, y, and z spatial locations) on the Earth's surface are determined.  NAD83 differs from NAD27 (datum of 1927) in that the NAD uses a different ellipsoid and has significantly improved accuracy.  It is not possible to use a simple conversion method between the two systems as the shift is inconsistent around the globe.
 

Briefly (1-2 sentences) describe your national or local coordinate system (State Plane Coordinate system or other) in your own words.

The State Plane Coordinate System (SPCS) divides the United States into about 120 zones, each determined by political boundaries whereby positions in the United States can be specified by a northing (meters north of the zone's origin) and an easting (meters east of the zone's origin).  Since the zones are relatively small, its accuracy is to about 1 part in 10,000.  But, because the zones are small, this system does not work well for maps covering large states, multiple states, or the entire United States.
 

Briefly (2-3 sentences) compare and contrast the three coordinate systems in your own words

The three coordinate systems all specify Earth locations as a Cartesian grid, taking a given position and giving it an x (east-west) and y (north-south) point from a given "origin." They each differ in the amount of inaccuracy they can introduce when used for a map.  Near the equator, distortion is low, but near the poles, distortion is extremely high.  For small areas away from the poles, SPCS is the most accurate  (up to 4 time better than UTM); but, SPCS cannot be used for very large areas, while the geographic coordinate system can be use to map the Earth, even though the distortion is higher as latitude increases.