Dory Kornfeld
Questions about Projections
April 14, 2009

1. When I changed the Projection to USA Contiguous Albers Equal Area Conic USGS, the shape of the map changed--it became longer and narrower, and rotated to a more north-south direction. The units displayed at the bottom right hand side of the ArcMap screen no longer gives the coordinates in degrees latitude and longitude because the Albers projection uses two reference latitudes, the numbers at the bottom of the screen are given in meters and reflect distance from the reference latitude.
 
 2. The projection that best represents the true area on the ground is the New York State Long Island projection. States have chosen their own projections that best reflect the truth on the ground--New York has two becuase it is an odd-shaped state, a different projection is selected depending on what part of the state you're representing
 
The most divergant projection (other than the unprojected calculation) is the Lambert projection.
 
I don't know why the unprojected calculation is so different from the rest.
 
Albers Equal-Area Concic Projection
-Minimizes distortion between the standard paralles
-does not preserve scale and shape
-equal area maps preserve area
-you'd use this to map British Columbia
 
Lambert Conformal Conic Projection
-Minimizes distortion, (but does not preserve area).
-conformal maps preserve angles
-Pilots uses Lambert projection maps because a straight line on a Lambert conformal conic projection is simmilar to a "great circle" route between departure and arrival points.
 
North American Equidistant Conic Projection
-preserves the distances from a standard point or line
-you'd use this to figure out how far away different things are from a certain point, such as how far various cities are from one specific city.
 
StatePlane New York Long Island FIPS
-stateplane maps are cartesian grids with a base point outside of the map so that all the numbers are positive.
-you use this for small portions of the earth--states, generally. This one for the long-island part of New York.

3. The UTM system is global while the State Plan system is just for America. The biggest difference between the two, however, is that the State Plan system is different for every state (sometimes different for different parts of states), and therefore not good for regional maps, while the UTM system divides the world up much more regularly, into 60 zones of 6° of width each.