III. Chapter 1.3

Representing Earth's Surface

Map ProjectionsA map projection is used to portray all or part of the round Earth on a flat surface. This cannot be done without some distortion.

Gerardus Mercator (1512-1594).

Map ProjectionsEvery projection has its own set of advantages and disadvantages. There is no "best" projection.The mapmaker must select the one best suited to the needs, reducing distortion of the most important features.

Map Projections

Mapmakers and mathematicians have devised almost limitless ways to project the image of the globe onto paper.

Map Projections

Scientists at the U. S. Geological Survey have designed projections for their specific needs—such as the Space Oblique Mercator, which allows mapping from satellites with little or no distortion.

The GlobeDirections—TrueDistances—TrueShapes—TrueAreas—True

The GlobeAdvantages:

The shortest distance between any two points on the surface of the Earth can be found quickly and easily along a great circle.The scale factor at each point is the same in any direction.

Disadvantages of the globe

Even the largest globe has a very small scale and shows relatively little detail. Costly to reproduce and update. Difficult to carry around. Bulky to store.

Global Grids--Longitude

The Earth is divided into 360 degreesCircumference lines run N—S and measure E—WThere are 360° in each day (0-180E and 0-180W=360° around the Earth)

Global Grids--Longitude

One hour = 15°0° longitude is called the Prime Meridian and is over Greenwich, England180° Longitude is the International Date line

Global Grid: Latitude

Circle the Earth going E—WMeasure N—S0° Latitude is the Equator

Global Grid: LatitudeThere are 90° in two latitudes: 0-90 N and 0-90 S a total of 180° (half circle)Tropic of Cancer: Latitude 23.3°NTropic of Capricorn: Latitude 23.5°S

Maps and Mapping:

No matter what type of map you use, there will always be some type of distortion of shape, size, distance or direction.

Mercator Projection (1569)Lines of longitude are parallel, making this grid rectangularDirections true

Distortion Increases away from Equator and is extreme in polar regions. Uses: for navigation and aviation

•Seagoing navigators still use the Mercator projection map.

Robinson Projection

Widely used due to little

distortion.Distances, area, sizes and shapes are accurateDistortion around map edges

•Uses: Maps in Goodes Atlas and by National Geographic

Conic Projection

Directions are true only from center point of projection.Distortion of shapes and areas increases away from center point.

Conic ProjectionThis type of projection is made by wrapping a cone of paper around a globe at a particular line of latitude.

•Uses: Road Maps and area maps

Gnomonic ProjectionsReliable and shows shortest distance between two pointsDisadvantage: Exact distance and directions are distorted

Topographic MapsShows Elevations of the landContour lines show the same elevations along the same lineContour index: Every 5th line is marked with the elevation