It appears to be using census data as aggregated by Wikipedia. At a glance that includes Portland, Lewiston, Bangor, as well as a number of "urban clusters" (I think I saw kennebunk and brunswick mentioned).
A lot of the places mentioned are not what I would consider urban(Berwick), but seem to be included due to their proximity to an urban area.
fissidens t1_j9z0vsw wrote
Reply to comment by MainerGamer in [OC] US states by urban population in %. by beastof_Bourbon
It appears to be using census data as aggregated by Wikipedia. At a glance that includes Portland, Lewiston, Bangor, as well as a number of "urban clusters" (I think I saw kennebunk and brunswick mentioned).
A lot of the places mentioned are not what I would consider urban(Berwick), but seem to be included due to their proximity to an urban area.