a couple of demographic facts:
manhattan's population swells from 1.5 to almost 3 million every work day.
DC's population from 580,000 to over one million.
in 1945, somewhere in the neighborhood of 80,000 people died from the initial blast, in a city with a population of only 250,000 at the time. the point?....population density. that weapon was somehwhere in the neighbourhood of 15kt...very small by most standards.
makes you want to move west.