Are there water shutoffs for whole neighborhoods or even wider areas?

I know each house has a shutoff, but when there's a huge water main break, how do they replace the water main? Can they shut off all the water to a whole area of a city/county? How many are there, generally? Every street, or just much wider areas?

Background: they're replacing the water main on our block and a few surrounding blocks, and they hooked each house into a pipe that runs along the edge of our property and gets its water from the fire hydrants. However, I can't imagine how they switch over from one source to the other. I know how hydrants turn on and off, but what do they do with the actual water main(s)? I can't imagine how these could be replaced under pressure.