ABSTRACT
In this chapter we outline the various issues involved in developing a three dimensional geographic information system (3dGIS) model for a large urban area, such as London. There are now many techniques which can be used to construct two-dimensional (2d) and threedimensional (3d) models of cities and their characteristics, which are useful for various types of visualisation. Until quite recently the main approach was based on rendering wire frame models of buildings based on Computer-Aided Architectural Design (CAAD/CAD). However, with the widespread development of Geographic Information Systems (GIS), there has been a move from the 2d map to the 3d block model which is based on extruding building plots, street line data, and basic topography. At the same time there has been a move towards the distribution of information relating to urban form and its representation via the Internet. Research at CASA into Internet based urban planning techniques has resulted in techniques whereby the common CAD based models of urban form can be adapted into a networked collaborative design and information system. A system which can be queried, explored and indeed inhabited through standard desktop machines linked to the Internet via standard dial up connections is currently being piloted.
