## GEOG 121 Project 1: Coordinates and Projections

Janet Beekman
The map projection that I choose is Mercator because this is what I'm most familiar with. The site I selected for this project is State College, PA, since I consider this to be my home town. The latitude and longitude of State College is 77.8608 degrees North and 40.7933 degrees West. The geographic coordinates of the projection center are 0 degrees latitude and 0 degrees longitude. With the Mercator projection, the lines of constant compass direction plot as straight lines. This projection distorts the areas of landmasses and other features. However, it preserves angle measurements and is called conformal. That is, an angle measured on on the projection is equal to an angle measured on the earth. I used the Weinelt, Martin(2002) Online Map Creation at http://www.aquarius.geomar.de/omc/ to create my map. I learned that west for longitude is also specified by a minus sign. I forgot this when I first tried to plot State College on the map. I had State College in several places until I got this right.

Geographic Coordinates
The place name shown on the map above represents the location of my home town, State College, PA. The geographic coordinates of my home town are:
Latitude: 40° 47' 36" N, Longitude: 77° 51' 37" W
The geographic coordinate system uses degrees of latitude and longitude to describe locations on the earth. Lines of latitude run parallel to the equator and divide the earth into 180 equal protions from north to south. Lines of longitude run perpendicular to the equator and converge at the poles. Longitude represents distance east or west from a starting point.

UTM Coordinates
The UTM coordinates (NAD83) of State College, PA are:
Easting: 258681.601 meters, Northing: 4519752.604 meters, Zone: 18
The UTM or Universal Transverse Mercator coordinate system, excluding the polar areas, divides up the globe up into 60 zones which are 6 degrees of longitude across the globe. The advantages of the UTM are the numbers of the coordinates are all positive, making computations simplier; the maximum error due to the map projection is low, and it is nearly global in extent. The disadvantage of UTM is that for large entities several coordinate systems must be used.
NAD83 is the North American Datum of 1983 based on the Geodetic Reference System of 1980. The measurements accurately represent the earth to within two meters. The NAD27 is the North American Datum of 1927 and is based on the Clarke ellipsod of 1866. NAD83 is more accurate than NAD27. The differences between NAD27 and NAD83 can be about 10 feet or as much as 200-300 feet.

State Plane Coordinates
The State Plane coordinates (NAD83) of State College are:
Easting: 590692.694 meters, Northing: 69599.990 meters, Zone: PA N
The State Plane coordinate system is made up of 122 different plane coordinate systems. These are accurate to 1 part per 10,000. The zones are based on either the Lambert Conic Conformal projection or the Transverse Mercator. To minimize distortion, wide zones use Lambert Conic Conformal and tall zones use Transverse Mercator. Both have the property of conformality, which means that the angles in the projection are equal to the angles measured on the Earth.

All three are used for specifing exact locations of the Earth on a map. Geographic coordinate system uses latitude and longitude while UTM and State Plane both use meters or feet. The UTM and SPC always have positive numbers which makes distances and directions easier to calculate. Computations of constant direction, shortest routes, and equal distances are hard to measure in the geographic coordinate system. Distortions in the UTM and the State Plane Coordinate System map projections make these computations easy to do. The State Plane Coordinate System is more accurate than the UTM system.

Sources
Dana, Peter H. (2000) Map Projection Overview http://www.colorado.edu/geography/gcraft/notes/mapproj/mapproj.html Accessed 24 August 2002.
DiBiase, David (2002) Understanding Geographic Data. Module 1: What Are Geographic Data? ESRI Virtual Campus http://campus.esri.com Accessed 23 July 2002.