Transcript Map Projections - Crescent School

Map Projections
Map Projections
What is a Map Projection?
Scale
Properties of Map Projections
Types of Map Projections
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
Distortions
• EVERY MAP PROJECTION DISTORTS AT LEAST THREE,
AND SOMETIMES ALL FOUR, OF THE FOLLOWING
PROPERTIES:
…
…
…
…
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.
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.
Once you reduce and flatten you need a scale to
convert measured distances on the projection to
actual distances on the real earth!
The three
scales in
action!
Properties of Map Projections
1. CONFORMAL:
…
2. EQUAL AREA:
…
3. EQUIDISTANT:
…
4. AZIMUTHAL:
…
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
• 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
Cylindrical Projections
Cylindrical Projections
Cylindrical Projections
Cylindrical Projections
Mercator Projection
Note: Most Topographic maps use a UTM
projection – Universal Transverse Mercator
Conical Projections
Conical Projections
Notice: this projection
preserves the shape or
conformal property
Conical Projections
Notice: this projection
preserves the distance
property
Planar or Azimuthal Projections
Planar Projections
Planar Projections
Planar Projections
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.
This is a Robinson projection and it is a
compromise between size and shape.
The shortest distance on a flat map is sometimes
not a straight line.
Discussion!
Another way at looking at Great Circles.
You can get some rather unusual projections.
Which distortion is greatest and which is the
least?
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/mapproj
/mapproj.html
The End!
The next slide show we should visit is the
one describing the different kinds of maps!