in case anyone wants to do a quick calculation of observation density for a place (or list of places), i made a page that can get place details, calculate the area of the place polygon stored in iNaturalist, get observation count for the place, and then figure out observation density.
page: https://jumear.github.io/stirfry/iNat_places.html
code: https://github.com/jumear/stirfry/blob/gh-pages/iNat_places.html
just for example, this will get place density for San Francisco, Hong Kong, and DC:
https://jumear.github.io/stirfry/iNat_places.html?place_id=san-francisco-county,district-of-columbia-us,hong-kong&stats=observations,density&verifiable=true. the calculated area will include both land and water. so it will calculate San Francisco’s area as ~600 sq km, which includes ~120 sq km on land and ~480 sq km in the water. that may skew the density figure of a mostly-water place like SF vs a mostly-land place like DC, which is ~180 sq km total, with ~160 sq km on land and ~20 sq km on water.
this page might also offer a quick way to get figures like those in https://forum.inaturalist.org/t/welcome-to-the-club-new-zealand/21711/7.