Moscow is also tremendously dense. It's sprawled out because it has so many people in it, but the vast majority of those people are packed into apartment buildings. The same goes for all other major urban centers. A typical Russian (or rather, ex-Soviet) cityscape looks like this, and can go for miles:

http://images.e-flux-systems.com/2014_04_Bric-III-Yugo-Zapad...

Now imagine an airburst nuclear explosion over this, just low enough to maximize the blast wave.

There's a reason why Soviets heavily invested into protecting the populace from such attacks - the entire Moscow Metro system doubles as a nuclear bomb shelter, complete with blast doors.