MAP PROJECTIONS but before let s review some basic concepts.

Transcription

1 MAP PROJECTIONS but before let s review some basic concepts.

2 Types of Maps General Purpose Topographic Thematic/Choropleth Dot Graduated Circle Isometric/Isolines Isopleth Mental Maps

3 Scale Small-scale map 1:250, 000 shows less detail of a large area! Large-scale map 1:50,000 shows more detail of a small area!

4

5 Latitude and Longitude

6 MAP PROJECTIONS Ø What is a Map Projection? Ø Properties of Map Projections Ø Types of Map Projections

7 What is a Map Projection? THE ONLY TRUE REPRESENTATION OF EARTH, FREE OF DISTORTION IS A GLOBE. MAPS 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 PROJECTION

8 Distortions EVERY MAP PROJECTION DISTORTS AT LEAST THREE, AND SOMETIMES ALL FOUR, OF THE FOLLOWING PROPERTIES: ü SHAPE ü AREA ü DISTANCE ü DIRECTION

9 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.

10 Properties of Map Projections 1. CONFORMAL: A CONFORMAL PROJECTION MAINTAINS SHAPE IN SMALL LOCALIZED AREAS 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: 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: THIS PROJECTION CORRECTLY SHOWS DIRECTIONS (AZIMUTHS) FROM A SINGLE POINT TO ALL OTHER POINTS ON A MAP.

11 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

12 Cylindrical Projections

13 Cylindrical Projections-The Map

14 Cylindrical Projections-The Map

15 Cylindrical Projections-The Map

16 Conical Projections

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

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

19 Azimuthal Projections

20 Azimuthal Projections The Map

21 Azimuthal Projections The Map

22 Azimuthal Projections The Map

23 Mercator Projection " Developed in the 16th century " Great for navigation because all lines of longitude and latitude are the same

24 Mercator Distortions: GREENLAND " Which is bigger Australia or Greenland? AUSTRALIA On the map Greenland. In reality, Australia is three times larger! " As you move away from the equator the map becomes more stretched

25 Peter s Projection " Created in the 1970s as an alternative to Mercator " Creator stated it was more neutral and less racist than Mercator

26 Peters Distortion " Which is bigger Australia or Greenland? On this map Australia is bigger, nation sizes are closer to reality " However the shape of nations is distorted " This projection is often referred to as hanging laundry GREENLAND AUSTRALIA

27 Robinson Projection " Created in 1963 " Purposely distorted to create a more pleasant appearance

28 Robinson Distortion: " The most popular and commonly used map projection " The major areas of distortions are at the poles " Still has a Eurocentric view of the world

29 Summary 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

30 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: Cylindrical eg. Mercator Conical eg. Lambert Planar 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 Conic

31 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 notes/mapproj/mapproj.html

32 The End!