Cities are the core game concept of Cities XXL. The player grows empty maps into cities, all of which are on the same Cities World planet.

City maps start out as bare terrain with untapped resources. The player adds zones for housing, industry, and commerce, while providing local infrastructure, including transportation, utilities and services. Each city can trade locally produced resources, known as tokens, either with other cities on the planet, or with Omnicorp, an entity that is always available to buy or sell any type of token for credits.