You should take into account humidity, seeing as the best humidity level at say 80ºF or even 70ºF is <i>very</i> much more pleasant than the worst.<p>Also, IMO your minimum temperature criterion is probably a mistake. Nobody cares that it's a little chilly at 4am, and meanwhile you're selecting for more humid climates (because those have less diurnal variation).<p>If you wanted to make the selection criteria user-adjustable, though, I'd be really interested to see the results. (Also, nice job on the visualization, discretizing every grid square to a town is particularly cute.)
Neat.<p>I was looking back at my last few years of utility bills recently and noticed that May (Avg: 60F) and October (Avg: 62F) are apparently the only months of the year where I don't feel a need to heat or cool the house.<p>If this were adjustable I'd be looking for the place with the most 60° days per year.