This ISIS Support Board is being retired. Please post all new topics to: https://isis.astrogeology.usgs.gov/fixit/ I have tried the projection file that ships with ArcGIS9.1 and the details it contains are quite different from the one available at Pigpen, as a result it has some funny effects when you load the Pigpen MOLA data up. The projection file that ships with ArcMap is just a definition of the size of Mars. Unfortunately, at the last minute, I decide to remove the the definition ‘Mars 2000 Sphere.prj’ from the definitions because it was not really an IAU approved system. Now I am kicking myself because it is an important definition to have. This is because it is safer definition to use when working with ISIS and ocentric latitude systems. Now this is only half the story. If you are working in a projection, the body definition is only part of the full projected definition. So the needed definition would have the projection spelled out like Equidistant Cylindrical, using a center longitude of 180 AND using the Mars 2000 Sphere.prj as the body. So you can only use the ‘Mars 2000 Sphere.prj’ if you are working in decimal degrees. If you are working in a projection, then you need the projection definition as well as the body definition. Source.