[LarryMade2]

And with that you can see in the beginning it wasn't all what it is now. It's been built up over the years, sometimes added to, sometimes totally refactored for better methods...

I would say the two things to make something complex is: to map out the data identify whats the core elements, and second, start building out from that. As you get the core stuff operational you can work on more bits and refactor, etc. As you build you will be coming up with problems and working out solutions, it's a process.

Also given the scale of Google Maps, from what it tracks and how many access it so many different ways, projects like that are the work of hundreds - many specializing on just one aspect or another.