You've probably heard the term "procedurally generated" thrown around gaming in the last few years. It's fancy tech, which at its most basic level means something that's built randomly each time you ask it to be built, but it's certainly more complicated than that, as content still needs to follow certain rules.
The best way to see how it works, then, is just to see it in action, which is exactly what Boids N' Buildings does. It's a program that, once activated, designs then builds a 3D city, which you're free to then move around using a variety of camera options.
It's the work of Singaporean animator zz85, who was inspired to create it after a trip to Tokyo, and once you watch it once, imagine this: there'll come a time in the not-too-distant future when you can press that "start" button, watch a city spring to life, then start playing.
Boids N' Buildings [Site]