Areas are regions of the map created by the world generator. An area defines what weather is common or even possible, what buildings will be generated, the zombie population density, and more. When a player starts up a new world in The Dead Linger, the world is randomly generated. The game is set in a non-specific place in the United States, and as such most areas are drawn from American geography. However, the game will have some natural features and buildings not typical of the US.
Confirmed areas
Suburbs
Suburbs are areas around cities which are less densely populated and have more open space. Suburbs contain widely spaced housing with yards around them, school districts, and small parks.
Cities
Cities are major population centers. They contain many different and large buildings, and the road makes up most of the open space available. A city contains skyscrapers and other large buildings, as well as industrial districts and city parks.
Rural areas
Rural areas are not very densely populated. They make up a lot of the inhabited area on the outskirts of towns. A rural area features farmland, cornfields, wheat fields, barns, farmhouses, and small roads. There is a very large amount of open space.
Forests
Forests are areas with a lot of trees. Forests are often on a slope, and consist of dense woods sprinkled with clearings. While few human zombies can be found here, there is a larger amount of zombie animals. Types of forest include national parks, deciduous forests, and pine forests.
Source: http://www.sandswept.net/forums/viewtopic.php?p=2140#p2140