Each Sim has a set plan each day: They wake up and pay their rent -- surprisingly, it's only $1 -- and go to work. After work, if they have money, they spend it throughout the region. Spending money gives Sims more happiness, thus increasing their enjoyment of your city.
Sims have their own bank accounts, and can potentially become homeless if they don't have any funds. If you don't have a place for Sims to earn money, they'll start loitering in parks, decreasing happiness and forcing them to move out of your city.
"Each Sim is carrying resources. Like that Sim there is a medium wealth, poorly educated Sim who's mildly sick, so he's going home from work early," Quigley said while pointing out a particular Sim during a gameplay demonstration of SimCity. "So he's not just a generic dot in your city -- he's a person who's left this place and is trying to go home." So initially, the life of a Sim is pretty basic, but as you add more variables -- buildings, parks, and other destinations -- the life becomes more complex.
Sims can also get in the way, too. Every car on the road is owned by a Sim and lives in a Sim's driveway. If a building is on fire and there's a traffic jam there, the fire trucks won't be able to get to the fire and the building will burn down. If an ambulance is going down a road and there's enough room, cars will pull over to the shoulder -- if it's a tiny road, then a Sim could die. So each Sim has a bearing on the city they're living in.
"Because it's SimCity, we have to be able to simulate thousands of Sims," Quigley noted as he showed off how the GlassBox engine simulates each Sim's life. "It's not SimHamlet -- it's SimCity. So we built this simulation engine to support many, many thousands, tens of thousands of Sims and vehicles in flight simultaneously. So each one of those Sims is a real Sim."
There are also unique Sim characters within the game. One such character shown was a firebug -- an arsonist rolling around town in a black van blaring metal music. He gets his kicks by going around, setting buildings on fire. If you don't have police to actually apprehend this guy, he could potentially burn your entire city to the ground. Quigley wouldn't detail other specific characters, but not every character will have a negative impact on a city.
"There's rich Sims, and there's poor Sims, and there are Sims on their way to work and there are Sims on their way to home after work; sims going shopping. Each one is a real Sim in your city," Quigley said. "At the end of the work day, the factory whistle is going to blow and you're going to see all of the workers leave the factory."
SimCity is expected to launch sometime in 2013.