Week 6 - Map Projections

Map projections vary because transforming a 3-dimensional spheroid into a 2-dimensional plane distorts certain portions of the 3-D surface in different ways (i.e. shape, distance, area, direction), depending on the projection.  Map projections are significant as they are created for different purposes and allow the map-user to use the best planar map for their specific intention, whether it be navigating across the sea or pin-pointing a target enemy.  Though 3-D maps (globes) are the best representations of Earth, they are not as functional as flat maps that can be transported, measured and reproduced as easily.  Globes also provide a general representation of Earth as a whole, whereas projections can not only be of the entire world (as shown here) but as more commonly fitted to different scales depending on what the map is going to be used for in order to provide the user a clearer representation of the particular area they are focusing on. 

For example, the conformal maps shown above are designed to preserve local shape and angular relationships by projecting the Earth with 90 degree angle, perpendicular graticule lines.  One of the most common conformal map projections is the Mercator map, which provides a grid map most commonly used for navigation, since it is more important to preserve angle relationships (that also preserve shape in small area scales) than preserving area when navigating across the sea. The Mercator map is an example of a cylindrical projection that preserves distance only along the equator, but distortion increases moving north and south from the equator.  Similarly, the Stereographic projection becomes increasingly distorted in terms of area and shape as one moves away from the center point.  These distortions are confirmed by the unusually high distance measured between Washington, DC and Kabul, Afghanistan (actual distance is closer to 11,000 km) in both of these projections.

Equal area maps are designed to preserve area, where all areas are reduced by the same scale and correspond proportionally with their counterparts that exist on Earth in reality.  Because of this, angles and shapes become distorted.  Equal-area maps are centered around central meridians (where distance is preserved) and become increasingly distorted as one moves away from the central meridian.  The Sinusoidal Equal-Area map is a common Equal-Area projection and is frequently used in atlases to show the distribution of countries when exact distances and shapes are not as important.  The distortion of distances is not as skewed as in the conformal map projections, but is still skewed in the higher latitudes, as shown by the higher than accurate distance between Washington, DC and Kabul in both the Sinusoidal and Hammer-Aitoff map projections.

The last of the three different types of  of map projections shown here are two types of equidistant map projections: the Two-Point Equidistant map projection and the Azimuthal Equidistant map projection.  Equidistant map projections preserve distance and direction only from the center of the projection or along a particular set of lines.  These types of maps are especially useful for airplane routes when centered on the city of origin, as it will then provide accurate distances and direction to any other location on the Earth. However, these maps are not useful in terms of identifying accurate shapes of locations as only the center point preserves area.  When projecting the entire world, as shown above, the equidistant map projections shows extreme area and shape distortion as one moves away from the central region (i.e. Australia in the Azimuthal Equidistant projection).  However, the Two-Point Equidistant projection did in fact display the most accurate distance between Washington, DC and Kabul, demonstrating it's usefulness in determining distance from a central point (it is off here since Washington, DC was not specified as the central point).

As demonstrated by these example maps, projections of the Earth display a wide variety of images used for very different purposes.  Choosing a projection is based on what feature is most important to preserve for your purposes, being area, shape, distance or direction.  Though some projections seem to display the Earth more 'normally' than others, it is important to remember that all 2-D representations show some type of alteration/distortion of Earth and it is significant to understand the manner in which the map was projected in order to identify exactly what it is that is most distorted.