Map Projections

Tools of Geography The most useful tool for looking at where things are in the WORLD is a globe It is an accurate, miniature of the actual earth It shows correct distance, size (area), shape, and direction

From Globe to Map Every flat map misrepresents the globe in one way or another—NO EXCEPTIONS! This is because the globe is a three dimensional object and maps are two dimensional EVERY MAP IS DISTORTED!!! Imagine peeling off an orange peel in once big piece. When you put it back together without the orange inside, it still forms a sphere. If you try to make it into a flat surface, the pieces tear apart.

Global Gores One way to try to overcome the problem of turning a globe into a flat map is global gores The globe is cut into sections to make the map However, the sections are still somewhat distorted Also, it is not very useful to read a map with gaps in the middle of places

So, how do they make maps? Through projections!!! Instead of “cutting up the globe,” they “project” it onto paper. Imagine a light bulb inside of the globe that casts shadows of land formations onto a piece of paper. If we trace the shadows, we have a map

Why are there different map projections? Depending on WHERE and HOW they hold the paper, we get different types of maps. Most common are cylindrical, conical, and azimuthal (planar) projections

Cylindrical Projections

Conic Projections

Planar (Azimuthal) Projection

Map Distortions Unfortunately, all maps are DISTORTED All maps have at least one distortion Four things get distorted on maps Some maps will distort some things and not others DISTANCE: How far apart things are SIZE (AREA): How big a place is SHAPE: What the form of a place looks like DIRECTION: Where places are in relation to each other; In other words, which direction should you REALLY go if you want to get somewhere?

Distance Distortion Unequal Equal Mercator

Size (Area) Distortion Miller Cylindrical

Shape Distortion Gall Peters

Direction Distortion Inaccurate Accurate

Three Categories of Maps Conformal: Show true SHAPES but distorted SIZES Equal-Area: Show true SIZE but distorted SHAPES Compromise: Show some SIZE distortion in order to portray shapes more accurately

Mercator Projection Conformal Map Used for navigation of ships Good: True direction shown at any two points on a straight line Bad: Size distortion at higher latitudes

Robinson Projection Compromise Map Uses: Educational materials Good: Reasonable overall picture of the world Bad: Distortion in polar areas

Azimuthal Projection Compromise Uses: Pilots use it to find the Great Circle Route (see next slide) Good: Shows accurate direction Bad: Distance and size distorted

Great Circle Route A great circle path is the shortest path on the surface of a sphere between two points on that sphere http://www.gcmap.com/ It is shorter to take a circle route and fly with the curve of the earth, than to take a straight line The great circle as plotted with 5° of longitude between the waypoints is 4627 M The composite route as plotted with 3° of longitude between waypoints is 4669 M. The rhumb line is 4843 M.