I think the lesson here is that 500 people per square mile is a very unnatural density- the largest-lot subdivisions will be higher, anything purely rural (even including hamlets, and in wet climates) will be lower. You need a hodgepodge to hit that mark.
You could end up with a 500 people per square mile density in an urban area if it's a mostly commercial district. There's a suburb in Minnesota with around that density that consists of a couple townhomes and a few car dealerships (the total population by the way is less than 500, minuscule place in both population and area.) Minneapolis' Downtown East neighborhood by the way has a density of 237 people per square mile.
To underline both points, here
another German example (view from ENE to WSW, older photo, probably from turn of the millennium, but the best I could find):
Definitely (sub-)urban according to demographic trends...
.. except for the fact that population density is being kept below 500 / square mile by
Using a parish-level approach, Großziethen (pop. 7,380, upper right corner of the older aerial photo above) would probably qualify as urban. Schönefeld proper (pop. 3,200, to the south of the Berlin border marked in red in the aerial photo below, airport area commences immediately south of the motorway) however, would still be counted as rural.
