[guard-of-terra]

This is only relevant for suburban (or village) style settlements.

For example, most of ex-USSR cities are built in huge 5-, 9- or 15-floor apartment blocks with lots of trees around them.

In this case, trees tell you nothing: there might be few trees because the part of the city is newly-built; there are no trees in historic inner city but it's usually the best and most expensive place. If there's a plenty of trees, it still tells you nothing.

[brazzy]

Even in Western Europe there was a period in the 1950s and 60s when city planners constructed high-rise satellite towns with lots of trees between the apartment blocks, pretty much all of which are mainly populated by poor people to this day.

[kalleboo]

Exactly. I think this blog post is an example where you can find whatever you want as long as you look for it.

Here's from Sweden.

Rosengård, one of the poorest areas in Sweden: http://imgb.mp/izU.jpg

Västra hamnen, full of expensive "eco-friendly" model apartments: http://imgb.mp/izV.jpg

[Someone]

An example: http://maps.google.com/maps?ll=52.318875,4.976646&spn=0....

#trees per person probably is a better metric. Band-filtered population density, as that filters out high frequencies due to local peaks and low frequencies that denote average wealth of a larger neighborhood, may be an even better one. I guess that might even work for extremely high-rise building as in Dubai. Firstly, the lower floors in such buildings typically are offices, and secondly, I guess the really high buildings will stand less close to other high buildings than the lower skyscrapers that surround it.

[guard-of-terra]

City center might have very low trees per person. Old, crumbling, partially deserted housing might have high trees per person.