Map Projections

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

What is a Map Projection? THE ONLY TRUE REPRESENTATION OF EARTH, FREE OF DISTORTION IS A GLOBE.THE ONLY TRUE REPRESENTATION OF EARTH, FREE OF DISTORTION IS A GLOBE. MAPS ARE FLAT – 2 dimensionalMAPS 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 PROJECTIONTHE 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: 1.CONFORMAL: … 2.EQUAL AREA 2.EQUAL AREA: … 3.EQUIDISTANT 3.EQUIDISTANT: … 4.AZIMUTHAL 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.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 preservedYou chose your projection based on the properties you want to preserve: equidistant – distance preserved conformal – shape preserved equal area – area preserved equal area – area preserved azimuthal – directions are preserved azimuthal – directions are preserved

Cylindrical Projections

Mercator Projection Note: Most Topographic maps use a UTM projection – Universal Transverse Mercator

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

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. 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 /mapproj.htmlDana, Peter H., “Map Projection Overview”, University of Colorado Boulder. (October, 2000): Online. Internet. Available at /mapproj.html

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