Pittsburgh’s 92 soils were classified into soil quality categories and mapped onto the same census tract map used in Section 2.1. Fig. 3a–d demonstrate the process of adding each soil layer to the map. Starting with the blank map (Fig. 3a), agricultural land,
greenways, and land with slopes greater than 15% were added in Fig. 3b. Urban soils were added in Fig. 3c and marginal soils were added in Fig. 3d. The total area of marginal land was then computed using GIS to intersect areas of marginal soil with areas of parcels with building footprints extracted. (For reasons of scale and clarity, parcels are not shown in Fig. 3.)