Rasters Methodology

Zoning Rasters are GeoTIFF files that summarize residential and nonresidential land-use regulations in 30x30 meter cells. They come in three versions: a GeneralRaster with up to 7 categories, a ResidentialRaster with up to 15 categories, and a Nonresidential Raster with up to 32 categories. The total number of categories present in any Zoning Raster depends on which land-use rules are in place in a given area.

The key input data source we use for constructing the rasters are Zoning Slices, which are the unique geometric combinations of base and overlay district regulations. Zoning Slices allow us to assign the most common residential and nonresidential use categories to individual raster cells.

The General Raster classifies cells by their zoning district type: Primarily Residential (housing is the main permitted use), Nonresidential (housing is prohibited as a principal use), and Mixed with Residential (housing is permitted alongside commercial and other uses). These use categories are defined in full here.

The Nonresidential Raster classifies cells based on the most common nonresidential uses permitted in a given Slice. For cells in Slices with a single nonresidential use, the nonresidential category is simply passed from the Slice data—as entered by the analyst into the NZA database in accordance with the NZA methodology—to the raster cell. For cells in Slices with multiple nonresidential uses due to there being one or more overlays, our classification schema determines which category best captures the most commonly allowed nonresidential uses in that cell.

When two or more nonresidential uses exist in the same cell, our method assigns the more general use. For example, cells falling within Slices where the nonresidential type is `Industrial` for the base district and “Mixed – Industrial-Commercial Uses” for the overlay district layer are assigned to the latter because “Mixed – Industrial-Commercial Uses” encompasses “Industrial”. Similarly, a combination of two nonresidential use categories in the same Slice can result in a third. For example, if the nonresidential type is “Industrial` for one layer and “Mixed – Specified Commercial Uses” for another, then the resulting classification becomes “Mixed – Industrial-Commercial Uses”. The one exception to this rule is that “Open Space/Light Recreation” uses always override other nonresidential uses because districts with this nonresidential type are frequently adopted for the specific purpose of disallowing other uses.

The Decision Tree shows the hierarchy of nonresidential uses specified by our method when a raster cell falls within a Slice with two or more nonresidential uses assigned to it. The Combination Matrix shows which nonresidential use category is produced from each possible combination of other nonresidential uses. “Open Space/Light Recreation”(Tier 1) overrides all. “Mixed – Any/All Residential” (Tier 2), as the most general nonresidential use category, comes next. Then, it is “Mixed – Industrial-Commercial Uses” (Tier 3).

Any combination of the Tier 4, 5, or 6 uses spanning both the “Industrial” and “Mixed – Specified Commercial Uses” branches reclassifies the cell up to “Mixed – Industrial-Commercial Uses”. Any combination of Tier 5 uses solely in the “Industrial” branch reclassifies the cell up to “Industrial”, while most combinations of Tier 5 and 6 uses in the “Mixed – Specified Commercial Uses” branch reclassify the cell up to “Mixed – Specified Commercial Uses”. The one exception is a combination of the lone Tier 6 use, “Research/Tech”, with its parent, “Institutional/Government”, which resolves to the latter.

Combination Matrix