People follow the plants. Or, at least that's what it looks like according to this plants hardiness map from by the government of Canada. Perhaps it comes as little surprise that the areas where vegetation thrives happens to coincide with the areas of highest habitation.
This map in particular combines information about a variety of climatic conditions across the entire country to produce a single map. The original was developed in the 1960's for trees and shubs. What plants grow where you live?