Spherical HEALPix projection onto the plane. Base‐resolution HEALPix pixels (indexed here from 0 to 11, as in the HEALPix software) project into 12 identical square pixels in the plane. Hierarchical subdivision of the HEALPix grid generates identical square pixel images over the entire planar image of the HEALPix tessellation (﹩N_{\mathrm{side}\,}=4﹩ pixel centers are shown within the base pixels 1, 6, and 10). Constant‐latitude lines map into horizontal lines on the plane (dashed lines), and the HEALPix spherical projection mapping of meridians on one hemisphere is shown by the dashed lines.