# Representing Earth's Surface

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Representing Earth's Surface
III. Chapter 1.3 Representing Earth's Surface

Map Projections A 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 ( ).

Map Projections Every 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 Globe Directions—True Distances—True Shapes—True Areas—True

The Globe Advantages: 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.

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 degrees Circumference lines run N—S and measure E—W There 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, England 180° Longitude is the International Date line

Global Grid: Latitude Circle the Earth going E—W Measure N—S
0° Latitude is the Equator

Global Grid: Latitude There are 90° in two latitudes: N and 0-90 S a total of 180° (half circle) Tropic of Cancer: Latitude 23.3°N Tropic 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 rectangular Directions 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 accurate Distortion 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 Projection This 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 Projections Reliable and shows shortest distance between two points Disadvantage: Exact distance and directions are distorted

Topographic Maps Shows Elevations of the land
Contour lines show the same elevations along the same line Contour index: Every 5th line is marked with the elevation