Explanation for online base maps

The Atlas of Mars examines the geography and geology found in each of 30 maps. We employ the Mars Chart, or MC, system of quadrangle maps originally created for the Mariner 9 images in the early 1970s. (We follow a common usage in geology, where the term "quadrangle" denotes any map sheet, even those not having four corners.) These maps cover Mars in 30 sheets originally at a nominal scale of 1:5,000,000, though published maps vary from this scale when matching along map boundaries is a priority. The Atlas of Mars uses a consistent numerical scale of 1:10,000,000 for overview and nomenclature maps and 1:20,000,000 for geologic maps. The plots employ Mercator projection scaled at the equator for sheets at 0 to 30 degrees latitude, Lambert Conformal projection for the sheets covering 30 to 65 degrees latitude scaled on standard parallels of 36.15 and 59.47 degrees, and polar stereographic scaled at 90 degrees latitude for the two polar sheets covering latitude 65 to 90. 

The overview map at the top of each set of maps uses the MOLA color hillshade data set, and the THEMIS daytime infrared mosaic (version 12.2) created for the Atlas of Mars is shown below. In this set of maps the overlay of names has been omitted. The polar sheets (MC-1 and MC-30) are divided in half, as was done to fit them on the pages in the printed Atlas of Mars.

These base maps should be printed at 100% size if maintaining the stated scale is a priority.

Kenneth S. Coles
31 August 2019

