Map Projections

1
Map Projections
2
Map Projections

• What is a Map Projection?
• Scale
• Properties of Map Projections
• Types of Map Projections

3
What is a Map Projection?

• THE ONLY TRUE REPRESENTATION OF EARTH, FREE OF
  DISTORTION IS A GLOBE.
• MAPS ARE FLAT 2 dimensional
• THE PROCESS BY WHICH GEOGRAPHIC LOCATIONS (LAT
  LONG) ARE TRANSFORMED FROM A 3 - DIMENSIONAL
  SPHERE TO A 2 - DIMENSIONAL FLAT MAP IS CALLED A
  PROJECTION

4
Distortions

• EVERY MAP PROJECTION DISTORTS AT LEAST THREE, AND
  SOMETIMES ALL FOUR, OF THE FOLLOWING PROPERTIES

5
Properties of Projections
The Cartographer decides on which projection to
use depending on which properties of the earth
are to be kept in the flat map. The following
slides will give you a more detailed idea of
these properties which will help you select the
best map for your particular purpose.
6
You cannot have a perfect projection. There will
always be some distortion. The Cartographer has
to decide which distortion he wants to correct at
the expense of another type of distortion.
7
(No Transcript)
8
(No Transcript)
9
Once you reduce and flatten you need a scale to
convert measured distances on the projection to
actual distances on the real earth!
10
The three scales in action!
11
(No Transcript)
12
Properties of Map Projections

1. CONFORMAL
2. EQUAL AREA
3. EQUIDISTANT
4. AZIMUTHAL

13
Types of Map Projections
Map projections are related to either a cylinder,
cone or plane. Imagine a transparent globe with
a light in the middle. You can project the globe
onto a flat sheet of paper just as a picture is
projected on a screen. In this case, because
the earth is round, the paper can be rolled into
a cylinder, a cone, or a plane. The projection
is made, and the paper is unrolled to reveal your
map! Even where you place the light source to
make the projection becomes an issue. Does the
light source go in the middle of the globe
(Gnomonic), touching the globe (Stereographic) or
off the globe altogether (Orthographic)? So, we
have three basic types of map projections 1.
Cylindrical 2. Conical 3. Planar
14
(No Transcript)
15

• A Cartographer decides which map projection to
  use for his/her purposes.
• You chose your projection based on the properties
  you want to preserve equidistant distance
  preserved conformal
  shape preserved
• equal area area preserved
• azimuthal directions are preserved

16
Cylindrical Projections
17
(No Transcript)
18
Cylindrical Projections
19
Cylindrical Projections
20
Cylindrical Projections
21
Mercator Projection
Note Most Topographic maps use a UTM projection
Universal Transverse Mercator
22
Conical Projections
23
(No Transcript)
24
Conical Projections
Notice this projection preserves the shape or
conformal property
25
Conical Projections
Notice this projection preserves the distance
property
26
(No Transcript)
27
Planar or Azimuthal Projections
28
(No Transcript)
29
Planar Projections
30
Planar Projections
31
Planar Projections
32
(No Transcript)
33
As mentioned earlier it is extremely difficult to
portray the whole world accurately on a map. In
the next slide compare the sizes of Antarctica,
Alaska and Greenland. In a (the Mercator
projection) the shapes are accurate but the sizes
are exaggerated. In b (the Eckert projection)
the sizes are accurate but the shapes are badly
distorted.
34
(No Transcript)
35
This is a Robinson projection and it is a
compromise between size and shape.
36
The shortest distance on a flat map is sometimes
not a straight line. Discussion!
37
Another way at looking at Great Circles.
38
You can get some rather unusual projections.
Which distortion is greatest and which is the
least?
39
References

• Most of the diagrams in this presentation were
  borrowed from the following website.
• Dana, Peter H., Map Projection Overview,
  University of Colorado Boulder. (October, 2000)
  Online. Internet.  Available at
  http//www.colorado.edu/geography/gcraft/notes/map
  proj/mapproj.html

40
The End!
The next slide show we should visit is the one
describing the different kinds of maps!