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Ch.5
Maps Projections
For cartographic representation purposes, it is necessary to project the points
recognized on the ellipsoid onto the map plane through appropriate analytical
transformations. As it is not possible to project or develop a spherical surface onto a
plane without altering the figure size and shape, every planar representation of the
Earth necessarily introduces distortion. It is possible to keep some characteristics
unaltered to the detriment of some others. According to the properties which are kept
unchanged, it is possible to define different types of planar projections:
Equivalent: maps which keep unaltered the ratio between the areas of the represented
surfaces. In these maps, equal areas on the map correspond to equal areas in reality.
Conformal or isogonic: maps which keep unaltered the angles between two directions
in reality and on the map. In isogonic maps, the angle between two directions in reality
is the same as in the map;
Equidistant: representations along a particular direction, such as the equator or a
meridian, along which the scale factor is kept constant;
Aphylaptic: maps which present all the alterations described above, but trying to keep
them as small as possible in size.
The following figures show some distortions caused by the cartographic
representations.

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