Map projections are ways of projecting a spherical surface, like a planetary body, onto a flat surface, like your computer screen. There are pros and cons to using any map projection. PDS MAP-A-PLANET supports three common map projections. These are listed below along with a little information about each one:
Simple Cylindrical: This projection works well for maps of the mid-latitude regions of the planet, distortion of the shapes of features increases as the map approaches the poles. Features on a planet, such as round impact craters, become flattened at the higher latitudes.
As the name implies, this projection represents perhaps the simplest of map projections. In this projection, lines of latitude and longitude are straight lines where the X-coordinate (left-to-right direction) on the map is proportional to the map longitude and the Y-coordinate (top-to-bottom direction) is proportional to the latitude.
Example of a simple Example of a simple
cylindrical projected image cylindrical grid
Sinusoidal Equal-Area:
In this projection, parallels of latitude are straight lines, with constant distances between equal latitude intervals. Lines of constant longitude on either side of the projection meridian are curved since longitude intervals decrease with the cosine of latitude to account for their convergence toward the poles. The Sinusoidal Equal-area projection is characterized by a projection longitude which is the center meridian of the projection. Areas remain equal size in this projection but feature shapes are distorted the further one goes from the central meridian and at the poles. In order to minimize map distortion, PDS MAP-A-PLANET always uses a center meridian at the center of the image map unless specified otherwise in the advanced options.
Example of a sinusoidal Example of a sinusoidal
equal-area projected image equal-area grid
Mercator: Mercator projection works very poorly in polar regions and becomes undefined at the north and south poles.
Historically Mercator is interesting because it is one of the oldest map projections to be used. Christopher Columbus used the Mercator projection in his travels to the new world. This projection is often used in navigation because any straight line is a rhumb line (a line of constant direction). Parallels of latitude and longitude are straight. Features increase in size as the map approaches the poles. Areas and shapes of large areas are distorted. Distortion increases away from the equator and is extreme in polar regions. However, being a conformal projection, angles and shapes within any small area are essentially true.
Example of a mercator Example of a mercator
projected image grid
PDS Imaging Node Homepage
The URL of this site is: http://pdsmaps.wr.usgs.gov/maps.html
Example of a simple Example of a simple
cylindrical projected image cylindrical grid
Example of a sinusoidal Example of a sinusoidal equal-area projected image equal-area grid
Example of a mercator Example of a mercator projected image grid
PDS Imaging Node Homepage
