"Education is the most powerful weapon we can use to change the world" Nelson Mandela

## Tuesday, 18 February 2014

### COMPARING PROJECTIONS

A globe is the only “perfect” representation of the Earth surface. All maps are distorted in four major ways. The four ways maps are distorted are by the distance, direction, area and shape.

 PROJECTION ROBINSON (pseudo-cylindrical) MERCATOR (cylindrical) AZIMUTHAL (aerial or polar) Geometric properties Conventional projection: don’t have “geometrical properties” (area, shape, distance, or direction) because it is not a geometrical projection, but seeks a compromise that minimize distortion over all. ·    Conformal: preserves shape (angles): meridians and parallels form straight angles and the scale is the same in all directions. ·    Equidistant. ·   Preserves directions (azimuths) from one or two points to the rest of points in the map. ·   Equidistant (the azimuthal equidistant projection): distances are correct along parallels. Picture Purpose ·   It was created to solve the distortions caused by Mercator & Peters projections. ·   Good for small-scale world maps, for general use because they look well. ·    Standard map for nautical, but it was started to be used to create world maps. ·   Its modified versions are widely used nowadays. ·    For showing airlines distances and for seismic and radio work. Distortion – types ·   Area: non equal-area projection or non equivalent. ·   Shape (angle) distortion (non conformal). ·   Area (size) distortion (non equal-area projection; non equivalent). ·   Shape (angle) distortion (non conformal). ·   Area (size) distortion. Distortion – Areas that are more distorted ·    Curved meridian avoiding opposite sides. ·   Straight parallels. ·   Stretched poles. ·   Severe polar distortion. ·   Important North distortion. ·   The middle map line isn´t established as it is the real middle line of the Earth (The Equator). It´s biased to the North. ·   Greenland appears with the same size as Africa, which is 14 times bigger. ·   Alaska... ... appears with the same size as Brazil, which is 5 times bigger. ... seems to be much bigger than Mexico, but it is actually just a little bit bigger. ·   Scale is different from the centre to the edge of the map. ·   The distortions increase as we go far from the centre of the map. ·   Meridians are straight. ·   Parallels are circular. There is more than one version? ·   Mollweide ·   Eckert ·   Sinusoidal ·   Pseudo-cylindrical Van der Grinten Projection (to correct latitude distortions). ·   Transverse Mercator. ·    Lambert azimuthal equal-area projection (preserves area) Sociocultural implications of using it as a learning resource ·   The map projection offers a complete look of the Earth, but shows the world as an oval and the poles are too distorted, they are so stretched than seem to be lines. ·   As the teacher gives the map to the students, they could infer that the North is bigger (and, consequently, more important, than the South) and that Europe is the centre of the world (because the unreal situation of the middle line, biased to the North, which makes Europe seem the centre). ·   On the other hand: it is useful to see the whole surface of the world. ·    If you want to study directions with your students, maybe it could be a good projection to use. ·   But they could not see clearly the whole world, just half of the earth.

So we can see that none of the maps is a perfect tool, they all have fails, distortions, and a teacher should explain, in a simple way or in a more elaborated one, depending on the student age, that, as the shadow of our body is distorting the real shape and are just a representation of the real body, maps projections cannot be identified to reality, they are just approximations to it.