Map Projections Geography Chapter 1 Intro

Globes are the most accurate maps, but they aren’t always the most practical What are some advantages and disadvantages of using a globe as a map? Advantage: Accuracy Disadvantage: Not enough detail to use for traveling

Map Projections A flat image is always more practical for a map than carrying around a big globe Cartographers convert the three dimensional globe image onto a two-dimensional flat map by making a map projection However, by losing that dimension, the projection is going to distort either the size, shape, distance, or direction The user of the map must decide which features are important and which don’t matter as much regarding their accuracy

Cylindrical Projection A cylindrical projection is made my taking a flat paper and folding it around the globe, into a cylinder

Mercator Projection The Mercator Projection uses a cylindrical projection Very popular among sea explorers of the 1500s, as it displays true direction But it does not portray shortest distance, and distorts the size on the top and bottom of the map (Greenland looks bigger than South America on this map) Note that the latitude and longitude lines are parallel, but longitude lines are not parallel on a globe, meeting at the poles

Sinusoidal Projection Sinusoidal projections are able to accurately represent the sizes of continents, but have to be cut up in order to keep the shapes accurate

Goode’s Map Goode’s Map is a famous sinusoidal projection (featured on the Goode’s World Atlas). The ocean has to be split to preserve the shapes of the land areas. Otherwise the areas would be accurate, but the shapes along the edge would be flattened.

Ecker’s Map Ecker’s Map is another sinusoidal projection. This one does not split the map in the oceans, but not doing so noticeably distorts the shapes of the land areas

Conic Projection Conic projections project the image onto a surface that has been formed into a cone

Lambert’s Map Lambert’s Map is a conic projection, popular map for airplane pilots, as a straight line on this map approximates the Great Circle Routes, which is the shortest distance to fly between two points

Great Circle A straight line on a globe looks like a curved line on most maps The curved line on this map is over 100 miles shorter than the straight line

Azimuthal (Planar) Projection An azimuthal equidistant projection, also known as a planar projection, projects directly onto a flat surface It shows distances and directions accurately from the center point, but distorts shapes and sizes elsewhere. Directions from a central point are preserved and therefore great circles through the central point are represented by straight lines on the map

Azimuthal equidistant projections are used by amateur radio operators to know the direction to point their antennas. This projection is used by the United Nations for its flag

Several maps try to combine the best of all maps, but their compromise does distort size, shape, and distance. But it’s a reasonable compromise Winkel Tripel Projection Robinson Projection

Map Projections Summary ProjectionExamplePicture of ExampleAdvantagesDisadvantages Cylindrical Mercator True direction, shapes are accurate Size of continents are distorted Sinusoidal Goode’sTrue area Have to split up the map to avoid distortion of shape Conic Lambert’s Great circles are straight lines on this map Can only see ½ of the world. Size and shape are distorted Azimuthal (Planar) Can point antenna based on this map. Center is accurate Sizes and shapes distorted away from center Composite Robinson’sA good compromise, so you get a generally good idea of size and shape So many compromises lead to no particular usefulness, other than aesthetics