Data Structures in UrbanSim

UrbanSim has evolved over several years, and so have the data structures used in it. Until 2005, most applications used a data structure based on a grid overlaid on the study area. Most UrbanSim applications do date have used this approach to structuring the data. Various limitations of the gridcell approach led to the more recent adoption of a parcel-based data structure. This section explains the fundamental differences in these data structures, and assesses their relative merits. Both are still used and supported approaches, though the advantages of the parcel approach are fairly significant.

In this chapter, the Puget Sound model application is used extensively as the basis for the description, in order to make the discussion more tangible. The study area for the Puget Sound model, now being brought into operational use by the Puget Sound Regional Council (PSRC), is the Central Puget Sound, consisting of King, Kitsap, Pierce and Snohomish Counties in Washington, as shown in Figure 2.2.

Figure 2.2: Puget Sound Region