Indeed, it doesn't seem to think that the fairly large cities of Vancouver, Calgary, Edmonton, Regina, Winnipeg, and Thunder Bay have a population of approximately zero. Anywhere in northern Montana has the "beam" shoot all the way over to Maine before reaching 100K, which isn't quite right since it passes through a couple medium Canadian cities and dozens of prairie towns.

I think this tool would be much more interesting in the western US if they had incorporated Canadian census data as well.

It does say that it only works in contiguous US (so no Alaska nor Hawaii nor "abroad" :D ), but seems it also works in Bahamas, for some reason, which as far as I know, isn't part of the contiguous US (yet?).