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San Francisco Digital Model
(continued)

The creation of SOM’s digital model began with an analysis of historical and present-day maps to build a consistent and accurate geographic basis for the model. The City of San Francisco’s Geographic Information Systems (GIS) database, which includes data such as locations and dimensions of streets, parcel lines, and blocks, was selected as the underlying structure. From the project’s inception, SOM decided that the 3D model would correspond directly to the 2D GIS data to simplify overlays of new geospatial data and future changes.

Because the GIS data is 2D and not intended for 3D visualization, the team then redefined the geometry of the streets and blocks to facilitate 3D operations. SOM created a curvilinear contour model of San Francisco and draped the 2D street grid over it, resulting in a 3D representation of the streetscape. The intersections were subsequently leveled automatically.

With this 3D groundwork in place, SOM then focused on the buildings. Because no database existed with comprehensive information on the City’s buildings, the team referred to aerial photographs, leasing plans, and design drawings to draw 2D outlines of building masses on appropriate parcels. Those outlines were projected onto the sloping ground planes and extruded vertically to create 3D buildings. Some of the buildings are simple box-like forms, while others are modeled in great detail.

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