For more detailed information about planetary nomenclature see Introduction to Gazetteer of Planetary Nomenclature.
You can now view the coordinates for Mars in two different systems: planetographic latitude with longitude increasing to the west, or planetocentric latitude with longitude increasing to the east. Both systems are approved for use on Mars by the International Astronomical Union (Seidelmann and others 2002).
Planetographic latitude with west longitude is the system that has traditionally been used for Mars, and was previously the only system used on this web site. Planetocentric latitude with east longitude has been adopted for use by the USGS and other organizations for use in making future Mars maps and imagery (Duxbury and others 2002). Since all previous martian maps (except for products produced by the Mars Orbiter Laser Altimeter (MOLA) Team (Smith and others 2001)) used the planetographic latitude with west longitude system, this system is being retained in the Gazetteer of Planetary Nomenclature for easy reference to maps produced prior to 2002.
Seidelmann (Chair), P.K., Abalakin, V.K., Bursa, M., Davies, M.E., De Bergh, C., Lieske, J.H., Oberst, J., Simon, J.L., Standish, E.M., Stooke, P., and Thomas, P.C., 2002, Report Of The IAU/IAG Working Group on Cartographic Coordinates and Rotational Elements of the Planets, and Satellites: 2000, in Celestial Mechanics and Dynamical Astronomy, v. 82, p. 83-110. Available from ADS.