Modeled Roughly on Nevin M. Fenneman's 1916 "Physiographic subdivision of the United States," subsequently called the "orders of relief," the orders of relief regionalization for Mars is organized around nested spatial scaling and the conspicuousness of features. The fifth order nests within the fourth order, which nests within the third order, which nests NOT within the second order but the first order. The second order is reserved for conspicuous features, each produced by a dominant geomorphic, climatological, or geological process. These are visually prominent enough to create an easy to remember general framework for the regionalization of Mars, which can then be used as a system of "landmarks" for situating other regions and features as one's mental map develops. The third order is implicitly temporal as much as spatial. The regions of the third order are differentiated broadly by the density of craters and their size distributions, which reflect the length of time a surface has been struck by bolides. Noachian regions exhibit the greatest profusion of craters and the greatest proportion of larger craters and date back before roughly 3.6 or 3.8 billion years ago. The majority of Mars' surfaces date from this early time. Hesperian regions are noticeably less cratered and show relatively fewer large craters, having been resurfaced by volcanic or hydrological activity more recently. These surfaces are younger than Noachian ones up to about 2.6 or 3.1 billion years ago. Surfaces younger than this are termed Amazonian and they display substantial modification and resurfacing, which have effaced the presence of craters: These show very few craters and these are overwhelmingly pretty small.

The first three orders of relief are plotted on the hypsometrically tinted map of digital elevation model produced by the Mars Global Surveyor's Mars Orbiter Laser Altimeter (MOLA), as shown and annotated with several region names below. To use the maps, first decide which level of detail you are interested in: the coarsest first order, the conspicuous second order, or the many medium to large regions of the third order. Click that link and the map will reappear, but this time hot-linked such that touching any spot will result in a map of the appropriate region and its boundaries. Most will be labeled as the map was built on a labeled map; some are not but the region's name will be found in the URL/filename. I will redo the labeling system at some point, as well as adding in the polar regions.

Enjoy your explorations!

• First order of relief
• Second order of relief
• Third order of relief