Map ProjectionsMap Projections

The Earth is a spheroid

A mathematical conversion must be used to create a flat map sheet from

the three-dimensional surface.

The Earth needs to be transformed.

Projection is a mathematical procedure of representing the

globe on a flat surface.

How do you put a round surface on a flat paper ?

• Mathematically, a projection is a process of transforming global location to a planar position.

• Planar coordinate systems:– Have two dimensions,

• X measures distance in a horizontal direction• Y measures distance in a vertical direction

– Measures of length, angle, and area are constant across the dimension

Different Acronyms

• UTM = Universe Transverse Mercator

• WGS = World Geodetic System

• NAD = North American Datum

• GRS = Geodetic Reference System

• Oblate Ellipsoid or Spheroid

The Earth is not a ball

• 1924 measurements were: e = 6,378,206.4

• P = 6,356,538.8 m• Or: f = 1/297

• 1980 (GRC80)– Geodetic Reference System

• 1983 (NAD83)• WGS84

– World Geodetic System

• F = 1/300p

e

F = 1-p/e NAD1927

(North American Datum)

Any representation of the earth’s surface in two dimensions:

• Causes some distortion:– 4 types of distortion:

• Shape

• area

• distance

• direction

• Different projections produce different distortions

Some commonly used map projections in the U.S. and North America

UTM a Planar Coordinate System

Latitude and Longitude

Latitude - Longitude

Is a geographic referencing systemNOT a projection

Mercator Projection

UTM Zone 13

Lambert Conformal Conic

Albers Equal-Area Conic

Miller Cylindrical Projection

MollweideProjection

RobinsonProjection