Using plans and regulations when making decisions about urban development requires access to the many plans and regulations of many different organizations, both private and public. Current information technologies, the Internet and the World Wide Web in particular, make access to data from such disparate sources feasible. Using these technologies to implement a `system of plans' approach to urban development planning will, however, require a widely shared data model for structuring the content and meanings of plans and regulations and a widely shared language, based on this data model. This paper presents an initial version of a planning data model (PDM), several use cases that set the scope of such a data model, and illustrations of how the current version of the PDM supports these use cases. Further work can build on this data model, including an XML (eXtensible Markup Language) implementation for sharing the information. These tools will enable urban development decision makers to conceive of planning as involving many actors whose many plans can provide useful and usable information.