The last task for the spatial allocation processing is creating the gridding intermediate files. The Grdmat program creates a gridding matrix (AGMAT, MGMAT, or PGMAT) and for on-road mobile sources an ungridding matrix (MUMAT). These matrices contain all of the factors needed to calculate gridded emissions from a source-based inventory. In addition, the Grdmat program writes a supplementary output file (AGSUP or MGSUP) that contains the spatial surrogates assigned for each source, indicates whether the assignment was a primary or a fallback, and identifies area-to-point sources. The structures of the SMOKE intermediate files output by Grdmat are provided in Section 9.4, “Grdmat”.