What If We Built a City on Mars?

The next step in space exploration isn't generations away. It's happening right now. And our destination? That mysterious, desolate world next door, Mars. Imagine starting life over on that tiny red dot over 265 million km (16.5 million mi) away. What would happen if we built a city on Mars? Would you have to live underground? How many people would you live with? And, what would the Martian economy look like? What does regolith have to do with living on Mars? How would radiation shielding be built?