Sustainability and protection of the environment are requirements of high priority in our society. These tasks need an efficient monitoring of the environment. The information gathered should be accurate and up-to-date for all kinds of decision making, planning, simulation and analysis. All environmental information systems are data-hungry and once established require continuous maintenance to keep track of changes in the physical environment. The built-environment is obviously one of the most interesting areas, with regular changes and constant need for updated information. An out-of-date database is arguably worse than having no database because of the false sense of certainty it carries. If there is no database, model etc. then at least users are aware of their lack of information and cannot rely on inaccurate data. In the context of these topics we are using the term ‘environment’ to denote the urban physical structures. We do not regard in this chapter applications related to the physical environment as it expresses itself in terms of different forms of pollution, e.g. noise, emissions, etc. Examples for those are given in several of the other chapters. We regard those applications as potential users of geo-spatial information on the built-up area of a city.