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Elevations were computed by subtracting the lunar reference radius of 1737.4 km from the surface radius measurements (LRO Project and LGCWG, 2008; Archinal et al., 2011). Thus elevation values are the distance above or below the reference sphere. The average accuracy of each point after crossover correction is better than 20 meters in horizontal position and ~1 meter in radius (Mazarico et al., 2012). The measurements were converted into a DEM (Neumann et al., 2011) using Generic Mapping Tools software (Wessel & Smith, 2008), with a resolution of 256 pixels per degree. In projection, the pixels are 118 meters in size at the equator. Gaps between tracks of 1–2 km are common, and some gaps of up to 4 km occur near the equator. DEM points located in these gaps in LOLA data were filled by interpolation Smith et al., 2010).
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