How do you unclaim a city in SimCity?

Solution 1:

There is no way to erase or restart a city without deleting the entire region.

Your best option is to start another city in the region, develop a stable economy, and then send a gift of §§ to the failed city to get it back on its feet.

If there are other players in the region that would like to try to salvage the city, you can open it up to them by Abandoning the city. You will lose Mayor status in that city by doing so.

From the Main Menu:

1. Click 'Play'
2. Select the 'Resume Game' tab
3. Select the region your city is located in.
4. Select the city you want to abandon.
5. Click the Abandon button.

Solution 2:

When I wanted to restart a city, what I did was to bulldoze all the services (anything that costs money) except the most important ones: power & water, as well as garbage & sewage (to avoid piling up pollution in the process). You should then be well in the green budgetwise, so you can simply wait until you have enough money (it can be the original 50k, but you can wait for more to make the rebuilding process faster), and then you bulldoze everything else (hold 'Ctrl' and aim for roads to make the process much faster). You'll have some buildings on fire; have to wait until they burn down to finish the process. Unfortunately, this won't give you back all the used resources (water, oil, coal, etc.), and if you had pollution, you'll have to let the city stand empty at max speed until the pollution is gone (ground pollution and radiation take a long time to wash out).