Map Projections

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Problem: The Golden Gate Bridge is located at latitude 37o 49' 11" N,

and longitude 122 o 28' 40" W. Convert degrees, minutes,

and seconds (known as sexagesimal system) to decimal

degrees and format the value for computer entry.

Solution: The whole units of degrees will remain the same (i.e., the

value will begin with 37). Minutes and seconds must be

converted to degrees and added to the whole number of

degrees.

Calculation: Latitude: 37o = 37o

49' = 49'(1o /60') = 0.82 o

11" =11" (1'/60")(1o /60') = 0.003o

37o + 0.82 o + 0.003o = 37.82o

37o 49' 11" N = 37.82o

Longitude: 122o = 122o

28' = 28'(1o /60') = 0.47 o

40" =40" (1'/60")(1o /60') = 0.01 o

122o + 0.47 o +0.01 o = 122.48 o

122 o 28' 40" W = 122.48 o

Answer: 37.82o, 122.48 o

5-13 Map Projections.

a. Map projections are attempts to render the three-dimensional surface of the earth

onto a planar surface. Projections are designed to minimize distortion while preserving

the accuracy of the image elements important to the user. Categories of projections are

constructed from cylindrical, conic, and azimuthal planes, as well as a variety of other

techniques. Each type of projection preserves and distorts different properties of a map

projection. The most commonly used projections are Geographical (Lat/Lon), Universal

Transverse Mercator (UTM), and individual State Plane systems. Geographic (Lat/Lon)

is the projection of latitude and longitude with the use of a cylindrical plane tangent to

the equator. This type of projection creates great amounts of distortion away from the

poles (this explains why Greenland will appear larger than the US on some maps).

5-5

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