For the purpose of making an Urban Ranger, does the Urban indoor and outdoor setting/location/place/area/space count as terrain for the purpose of the Rangers Natural Explorer ability? I'm using the revised Ranger from Unearthed Arcana.
The Natural Explore ability is unrelated to terrain. Unlike the PHB, an UA ranger does not have associations with particular terrain types.
The first 3 abilities function all the time anywhere. The remaining abilities apply when "navigating the wilderness". The relevant Miriam-Webster definition of wilderness is:
1 a (1) : a tract or region uncultivated and uninhabited by human beings (2) : an area essentially undisturbed by human activity together with its naturally developed life community
b : an empty or pathless area or
c : a part of a garden devoted to wild growth
On the face of it, urban areas and buildings are not wilderness. However, abandoned urban areas and buildings could be.