MAP PROJECTIONS

 What is a Map Projection?  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.THE ONLY TRUE REPRESENTATION OF EARTH, FREE OF DISTORTION IS A GLOBE. MAPS ARE FLATMAPS ARE FLAT PROCESS BY WHICH GEOGRAPHIC LOCATIONS (LAT & LONG) ARE TRANSFORMED FROM A 3 - DIMENSIONAL SPHERE TO A 2 - DIMENSIONAL FLAT MAP IS CALLED A PROJECTIONPROCESS 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: SHAPE AREA DISTANCE DIRECTION

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.

Properties of Map Projections 1.CONFORMAL: 1.CONFORMAL: A CONFORMAL PROJECTION MAINTAINS SHAPE IN SMALL LOCALIZED AREAS 2.EQUAL AREA 2.EQUAL AREA: THESE PROJECTIONS SHOW THE AREAS OF ALL REGIONS ON THE MAP IN THE SAME PROPORTION TO THEIR TRUE AREAS ON THE GLOBE. 3.EQUIDISTANT 3.EQUIDISTANT: NO MAP CAN SHOW DISTANT CORRECTLY BETWEEN ALL POINTS ON A MAP, BUT ONLY FROM ONE, OR AT MOST TWO, POINTS TO ANY OTHER POINT. THIS PROJECTION MAINTAINS DISTANCE. 4.AZIMUTHAL 4.AZIMUTHAL: THIS PROJECTION CORRECTLY SHOWS DIRECTIONS (AZIMUTHS) FROM A SINGLE POINT TO ALL OTHER POINTS ON A MAP.

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

Cylindrical Projections

Cylindrical Projections-The Map

Conical Projections

Conical Projections – The Map Notice: this projection preserves the shape or conformal property

Conical Projections – The Map Notice: this projection preserves the distance property

Azimuthal Projections

Azimuthal Projections – The Map

Summary 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

Summary You then decide on which type of projection you want. This depends on which area of the earth you want to display and how you want to display it:You then decide on which type of projection you want. This depends on which area of the earth you want to display and how you want to display it: Cylindrical – eg. MercatorCylindrical – eg. Mercator Conical – eg. LambertConical – eg. Lambert Planar – eg. AzimuthalPlanar – eg. Azimuthal Each type of projection is associated with many different projections that preserve different properties. They each get their own name. For example, there is a Lambert Conformal Conic AND a Lambert Equidistant ConicEach type of projection is associated with many different projections that preserve different properties. They each get their own name. For example, there is a Lambert Conformal Conic AND a Lambert Equidistant Conic

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

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