object: A ubmsFit model with a spatial random effect
param: The parameter to plot, either "state" for, e.g., mean occupancy or abundance, or "eta" for the random effect itself
sites: If TRUE, also plot the locations of sites that were sampled on the map and if had a detection of the species
cell_size: The size of each side of the (square) cells drawn in the map, in the same units as the coordinates. If NULL, ubms will try to pick a reasonable cell size for you