Lab 5: Projections in ArcGIS

 

Getting Started Questions:
How many degrees does the equator span?
360 decimal degrees
How many degrees do the northern- and southern-most graticule lines span?
180 decimal degrees

What do these two lines in fact represent?
These two lines represent the total distance in decimal degrees around the Earth latitudinally and longitudinally.

Approximately how many miles separate Washington, D.C. and
Afghanistan when crossing the Atlantic?
6,913.151 miles

Mercator Projection: 
Is Alaska really bigger than Brazil?

Yes

What about Greenland?

Yes

How far is Washington, D.C. from Kabul now?

10,110.689 miles 

Map projection is essential in creating maps as it allows a better understanding of the three-dimensional world by representing it on a two-dimensional surface. It also provides a more transportable model as well. Cylinders, cones, and planes are all used to create map projections. Map projections are constructed to preserve one or more of the map regions properties including area, shape, direction, bearing, distance, and scale. Different map projections exist depending on the purpose but no map can perfectly represent the surface of the entire Earth.

Equal area projections such as the Bonne projection and the Sinusoidal projection preserve area. They keep the areas on the Earth and their corresponding areas on the equal area map proportional. In other words, given any two regions A and B on the Earth and their corresponding regions A' and B' on the map, the surface ratios of A to A' and B to B' are the same.

Equidistant projections preserve distance from some standard point or line. These include the equidistant cylindrical projection and the equidistant conic projection. They maintain equal distances from the center of the projection to any other place on the map in all directions, but area is distorted as a result.

In conformal projections such as the Mercator projection and the Gall Stereographic projection, angles are preserved locally. The Mercator projection is the most widely-used conformal projection. It is a cylindrical map projection and is used for nautical purposes because of its ability to represent rhumb lines as straight segments. It is good for preserving the angles and the shapes of small objects, but it distorts the size and shape of large objects as the scale increases from the equator to the poles.

Map projection is the method of taking the surface of a sphere or other shapes and representing it on a plane. Inevitably, distortions occur during the transformation of a 3-D model to a 2-D surface and some information is lost in this process. Despite these perils, map projection is significant in creating maps and its variablility allows the user to choose and construct the best-possible representation of the desired model depending on the situation.