Lab 5: Projections in ArcGIS

GCS & Mercator Map Projection

The first depiction of the world shown is drawn from the geographic coordinate system.  GCS is different from a projected map because GCS is a coordinate system based on a three-dimensional model of the Earth not a projection system, so when GCS is put directly on a two-dimensional map distortion occurs.  The second map is a Mercator map projection, which is a cylindrical map projection and is conformal meaning that all angles are preserved but distances and areas are distorted.  In the Mercator map, the world looks like a vertical rectangle with land to the far south and north (e.g. Greenland, Antarctica) especially stretched out vertically.  The measured distance from Washington D.C. to Kabul is significantly longer on the Mercator map projection than on the GCS map, about 10,100mi compared to 7,000mi.

Cylindrical & Bonne Equal Area Map Projections

The cylindrical equal area map projection is a cylindrical map projection that makes the world look like a rectangle on a two-dimensional map.  Everything appears to be stretched out from east to west, and the measured distance from Washington D.C. to Kabul is longer than on the Bonne map projection below, about 10,100mi compared to 6,700mi.  The Bonne equal area map projection is a pseudoconical map projection that makes the world look heart-like in shape.  In both map projections, area is preserved but angles and distances are distorted.

Conic & Cylindrical Equidistant Map Projections

The equidistant conic map projection is a conic map projection in which distances along the meridians are preserved, but angles and areas are distorted.  The equidistant conic map projection makes the world look like a circle with a wedge removed (or a pizza with a slice removed) on a two-dimensional map.  All continents beside Antarctica look small and somewhat compressed, but Antarctica stretches all the way around the map projection in a strip.  The equidistant cylindrical map projection is a cylindrical map projection in which distances along the meridians are also preserved but angles and areas are distorted.  This map projection, however, makes the world look square-like in shape, reminiscent of the Mercator map projection in appearance.  The measured distance from Washington D.C. to Kabul is shorter on the equidistant cylindrical map projection than on the equidistant conic map projection, about 5,100mi compared to 7,000mi.