When my wife and I lived in Bristol we developed a metric designed to measure how enjoyable a city was to live in that we called "time to sheep". Basically it's a measure of how long you have to travel from the center of the city before you're in the English countryside surrounded by sheep and the best cities have a low (but not too low) "time to sheep" metric. It helped explain one of the reasons we loved living in…
If your metric is time or distance to large amounts of nature, I recommend Ottawa, Canada where the 140 square mile Gatineau Park starts 5 miles from downtown.
Toronto sucks for this :((.
Also time is probably a better metric. You can sit in traffic for an hour to move less than 1km.