These maps show the number of species in each group that were ever observed on individual BBS routes. Consequently, the maximum number of species on each maps is limited to the number of species in the species group. As with the relative abundance and trend maps, species richness maps are smoothed using inverse distancing.
These maps are all underestimates of the actual species richness! Species are always "missed" on counts, hence these maps must be viewed as minimum estimates of richness. However, they do show the relevant regional patterns of species richness.