by Jim Riesterer . . . . . . . . . . Edited by Scott Hughes, Dan Narsavage & Diana Boyack
Topographic Maps Tutorial
Introduction & Materials
What is a Map?
Using Topo Maps
Map Scale
Reference Datum
Map Projections
Distortions
Grid Systems
Geographic
UTM
State Plane
Public Land Survey
Vertical Scale
Creating Profiles
Vertical Exaggeration
Calculating Slope
Using a Compass
Magnetic Declination
Get a Bearing
Go from A to B
Find Self on a Map
Topographic Maps Field Exercises
Exercise 1
Exercise 2
Exercise 3
Exercise 4
GeoSTAC Home
Field Exercises
geostac@gmail.com
April 7, 2008
Map Projection Distortions
Each of the different types of projections have strenghts and weaknesses. Knowledge of these different advantages and disadvantages for a particular map projection will often help in which map to choose for a particular project. The basic problem inherent in any type of map projection is that it will result in some distortion of the ‘ground truth’ of the area being mapped.
There are four basic characteristics of a map that are distorted to some degree, depending on the projection used. These characteristics include distance, direction, shape, and area. The only place on a map where there is no distortion is along the trace of the line that marks the intersection of our ‘paper’ with the surface of the earth.
Any place on the map that does not lie along this line will suffer some distortion. Fortunately, depending on the type of projection used, at least one of the four characteristics can generally be preserved.
A conformal projection primarily preserves shape, an equidistant projection primarily preserves distance, and an equal-area projection primarily preserves area.
These image show the earth using different projections. Notice how the continents look stretched or squashed depending on the projection. Following are some websites with more information.