I like to use wildlife as a proxy for the quality of a location. If you can see things like rabbits and squirrels on a regular basis, you are probably doing reasonably ok. I have to put up fences and other barriers or the deer will eat everything in my yard.
I've seen suburban development that would easily satisfy the three tree test from any window on any property, but they still come off as desolate wastes. The age of the trees seems to be a non trivial factor.
Yeah wildlife & its variety is a good indicator for how much an area is disturbed by humans.
For this reason, I'd prefer to have compact cities with a good amount of high-rise buildings and city parks dotted in between. As opposed to large sprawling suburban zones.
That leaves more space for natural areas outside cities where people are few & far between.
@steerpike on HN coined the "time to sheep" metric, a measure of how long you have to travel before you're surrounded by sheep[0], which correlates reasonably well with quality of living.
Alas, doesn't work very well outside of britain, but it's a good metric :)
[0] https://news.ycombinator.com/item?id=42802744
Anywhere tropical is pretty far out from sheep, so that metric is clearly broken.