Case Study:

Envision Utah

Methodology

Raster GIS Environment

The key to the land use analysis was the use of Spatial Analyst, a raster-based module of ArcView GIS software. It can be thought of as an extensive, geographically referenced spreadsheet with rows and columns of cells containing data corresponding to the layer. The raster environment allows multiple data layers to be quickly combined into composites, making it an efficient tool for large-scale modeling. The modeling utilizes a 50.3-meter (156-foot square) grid cell for the analysis, so that one square mile contains exactly 1,024 cells. Given the level of analysis in the first phase of Envision Utah, this provided sufficient resolution for the comparative models.

The gridding of data into a common raster environment provided the foundation of the Envision Utah scenario analysis and also facilitated other components of the analysis. Analysts with Utah's Automated Geographic Reference Center (AGRC) felt that while some of the analysis could have been performed with GIS data in a vector environment (polygons), it was more efficient in a raster environment. Logistically, converting polygon to grid data is a relatively simple process, but it requires a knowledge of how to work with the data. For example, census tract population data must be converted to densities, which are then assigned to associated raster cells and converted back to population. According to AGRC, working with GIS data to the extent undertaken in the Envision Utah analysis requires a "sophisticated and trained GIS technician."

A GIS raster environment has also been applied by the State of Oregon for statewide land use forecasting, and in the analysis of regional scenarios in a number of European cities (see SPARTACUS case study).

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