Is there a geographic limit of cool?

Is it just coincidence that the most interesting parts of New York, Dallas, and Chicago are approximately two miles wide by six miles long?

I'm thinking Manhattan from the Battery to Central Park North, North Dallas / Park Cities from Uptown to the LBJ, between the Tollway and Central, and Chicago North of the river to Evanston, between the river and the lake.

Maybe it's a numbers thing. (or an American thing.)