City planning comprises many tasks: Constructing residential areas, designing commercial and industrial areas, areas for public interest and for transportation, waste management, and a lot of environment related tasks.

As defined by the german Basic Law, the Grundgesetz, it is up to the town to fulfill these functions (Art. 28 GG). Every commune has the right to decide of their own future development. At the same time, it's also their duty to design land-use plans (zoning plans as well as smaller scale land-use plans), "as soon as they become nesessary for the urban development and order" (§ 1 (3) BauGB). Land-use planning is a town's most important instrument: It defines where and at which scale a certain land use is supposed to be realised.

This is why planning must fulfill the citizens' needs. It is the town's administration that decides when plans are made, modified and abolished. But because economical, political and social interests in the urban landscape and in land-use differ, it is the task of the planners to find a solution to those problems.

To find that solution, city planning must weigh up the various arguments and needs that exist among an urban society (§ 1 (7) BauGB). To achieve that, the citizens' interests in a certain plan are gathered and analysed. By considering the citizens' suggestions and opinions, planning tries to find the best solutions for the urban community.

Planning must take into account the laws at the various levels, the ordinances, reglementations and statutes. But it must also consider the town's built environment, the history, the climate, the topography and the environmental conditions.

While federal law and the law of the Laender are the legal base for decision-making, it is the preparatory zoning plan that provides the narrowest definition of possible actions, just as the land-use plan. The communal administration itself created those plans and defined their contents, and is now forced to comply to its own objectives. If the town diverges from its own plans, the process of planning under public participation must be repeated