Map Projections

Tools of GeographyThe most useful tool for looking at where

things are in the WORLD is a globeIt is an accurate, miniature of the actual earthIt shows correct distance, size (area), shape,

and direction

From Globe to MapEvery 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 dimensionalEVERY 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 GoresOne way to try to overcome the problem of

turning a globe into a flat mapis global gores

The globe is cut into sections to make the map

However, the sections are still somewhat distorted

Also, it is not very usefulto read a map with gapsin the middle of places

So, how do they make maps?Through projections!!!Instead of “cutting up the

globe,” they “project” it ontopaper.Imagine a light bulb inside of

the globe that casts shadows of land formations onto a piece of paper.

If we trace the shadows, wehave 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 DistortionsUnfortunately, all maps are DISTORTEDAll maps have at least one distortionFour things get distorted on mapsSome 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 MapsConformal: 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 ProjectionConformal MapUsed for navigation of ships

Good: True direction shown at any two points on a straight line

Bad: Size distortion at higher latitudes

Robinson ProjectionCompromise Map Uses: Educational materials

Good: Reasonable overall picture of the world

Bad: Distortion in polar areas

Azimuthal ProjectionCompromise Uses: Pilots use it to find the

Great Circle Route (see next slide)

Good: Shows accurate direction

Bad: Distance and size distorted

Great Circle RouteA 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.