Introduction to Projections week 5

A map projection is the result of transforming 3 dimensional earth to a 2 dimensional map. Different projections have different distortions.  This could be partially due to the developable surface (plane, cylinder or cone). The developable surface could be tangent (touching) or scant (intersecting).  The farther from the tangent or scant the data the greater the distortion.  Map projections can have some but not all: true directions, true distances, true areas, true shape.  Consistent projections are important in datasets to ensure accurate analysis (don’t want to be comparing apples and oranges).

This weeks map and included table highlight four Florida Counties to be compared in three projections.

 Albers, a dual line conic projection, is said to accurately represent area.  UTM, Universal Trans Mercator, is a cylindrical projection from a meridian (N/S), area and shape are distorted as distance from the meridian increases.  State Plan is not a projection but a coordinate system that then uses a projection, in this exercise it is Lambert Conformal Conic, that strength lies more in shape than area.  In the comparison of the exercise UTM 16 N shows the greatest distortion in Miami-Dade county and almost no distortion in Escambia county.  Escambia county is nearly centered horizontally within the projection area of 16.  Miami-Dade is in UTM 17 – farther away from area 16 and therefore more distortion.