Lap #4 Working with Map Projections

Geog 206

Stefanie Wieschalla

Part 1: Map projections

Part 2: Significance of Map Projection

One might wonder why people need maps if a good globe can offer the most accurate representation of the earth. However, what is often forgotten is that a globe is actually not useful for many of the purposes for which we need maps. Map projections are necessary for creating maps thus maps could not exits without map projections. They permit us to represent some or the earth’s entire surface, at a large range of scales, on a flat, easily movable surface like for example, a sheet of paper. Map projections are more compact and easier to store, they can facilitate measuring properties of the terrain being mapped and they can show larger portions of the earth's surface at once. Besides that, they are cheaper to produce plus transport and they can further be applied to digital map data, which can be represented on a computer display. These useful traits of maps motivate the development of map projections. Today there are surely hundreds of different map projections to choose from. Each of them has its own strengths and corresponding weaknesses given that the process of transmitting information from the earth to a map causes every projection to distort at least somehow. Generally, distortion takes place in shape, area, distance and/or direction. Hence, every projection has its own advantages and disadvantages. There is simply no best projection because the appropriate projection for any given map depends on the scale of the map plus the function for which it will be utilized. For example, a projection could have intolerable distortions when used to map the entire United States, but may actually be a great alternative for a large-scale detailed map of California. Additionally, the properties of a map projection can also affect some of the design attributes of a map. Some projections are for instance clearly good for small areas, but some are not. It is also important to keep in mind that there are many ways to categorize the large variety of map projections. One of the most common classifications is by distortion characteristics. One need to question which properties of the earth does the projection maintain and which does it distort. A projection that maintains precise relative sizes is referred to as an equal area. Equal area projections are used for maps that indicate distributions or other occurrences where representing area accurately is significant. However, shape, distance and direction are distorted, especially when getting closer to the poles. Examples of the maps I used are the Gall Stereographic Projection and the Bonne Projection, which both indicate that the approximate distance between Washington, D.C. and Baghdad is about 5,970 miles. Now, a projection that preserves angular relationships and true shapes over small areas is called a conformal projection. These projections are generally utilized for navigational charts since angular relationships are important. Yet, distortion of area and direction increases away from the equator and is extreme in polar regions. Examples that I used for the assignment are the Mercator projection and the Eckert 1 projection. The estimated distance from Washington, D.C. to Baghdad varies in both examples. The Mercator projection approximates the distance to be about 8,389 miles, where the Eckert 1 projection indicates it only as 6,161 miles. The last two map projections that I choose where examples of equidistant projections, which maintain accurate distances from the center of the projection or along given lines. The projections are used for radio and seismic mapping and for navigation. However, shape, area and direction are, even though constant along any given parallel, quite distorted when the distance from the standard parallels increases. The examples I applied are the Equidistant Conic and the Equidistant Cylindrical projection. The estimated distance from Washington, D.C. to Baghdad varies in both examples again. Where the Cylindrical estimates to distance to be only 4,212 miles, the Conic indicates the distance to be around 6,277 miles. Initially, a map projection may also combine several of these characteristics or could be a compromise that distorts all the properties of shape, area, distance and direction within some tolerable limit. Even though not needed for the map exercise, a good example would be the Robinson projection, which is often used for world maps.

Part 3: Coordinate Systems & Projections Worksheet

1. An ellipsoid is a mathematical surface that is characterized by rotating an ellipse around its minor/polar axis. The ellipsoid estimates the surface of the earth without “topographic undulations”. The ellipsoid differs from a sphere given that it is slightly flattened at the poles.

2. The imaginary network of intersecting latitude and longitude lines on the earth’s surface is called a “Geographic Coordinate System”.

3. In contrast to the geographic North Pole that is located at the northern pole of the earth’s axis of rotation, the Magnetic North is the direction where a compass points to. It is important to realize that they are not at the same place at any point in time.

4. Datums are important because they tell one the latitudes and longitudes of a set of points on an ellipsoid, in order to determine surface locations. Datums are developed by determining a set of points by which all other latitudes and longitudes are established. One can determine these points through “geodetic surveys and monument points”.

5. A map projection is the alteration of coordinate positions from the earth’s curved surface onto a flat map. Points are “projected” from the earth surface and onto the map surface.

6. A developable (flat) surface is a geometric shape onto which the earth surface locations are projected. Common examples would be cones, cylinders, and planes.

7. d.) Lines of Latitude run north-south, converge at the poles, and mark angular distance east and west of the prime meridian.

8. a.) Clarke 1866 is now regarded as the best model of the earth for the region of North America.

9. For developing and analyzing spatial data when mapping countries or larger area it would be appropriate to use the Universal Transverse Mercator coordinate system given that it is a global coordinate system and it divides the earth into zones, which are each 60 degrees of longitude wide. Furthermore, the UTM zones have a large width that is necessary to accommodate large area analyses since all regions for an analysis are must be in the same coordinate system if they are to be analyzed together.

10. A great circle distance is a distance measured on the ellipsoid and in a plane through the earth’s center.