Jennifer ObadiaJanuary 25, 2008
Project: The Diggable City: Making Urban Agriculture a Planning Priority
Project Website:
Researchers: The DiggableCity was a project undertaken by several masters students at the Nohad A. Toulan School of Urban Studies and Planning at Portland State University (PSU). The research team included Kevin Balmer, James Gill Heather Kaplinger, Joe Miller, Melissa Peterson, Amanda Rhoads, Paul Rosenbloom and Teak Wall.
Purpose: In November 2004 the city council of Portland, Oregon passed a resolution requiring multiple city bureaus to conduct an inventory of their properties in order to assess which lands may be suitable for agricultural uses. Students from the Urban and Regional Planning Program at PSU worked with the Bureau of Environmental Services (BES) and the Bureau of Parks and Recreation, Water Works, and the Office of Transportation (PDOT) to complete the inventory.
The primary goal of this project was to assist the city in expanding and improving opportunities for urban agriculture in the city of Portland.
Data and Methodology: GIS data was provided by the various city agencies with which the research team worked. It is unclear from the report when the bureaus originally collected their data.
The datasets were clipped to remove environmental overlay zones and developed areas. The files were then analyzed with one-foot aerial photographs to assess for tree canopy, buildings and parking lots. Based on these characteristics and a visual assessment, each lot was assigned to an agricultural type category. Despite some qualities that may make a site unsuitable for agricultural purposes they have not been removed from the database.
The agricultural categories include:
1)Small-scale agriculture – pervious surface layer less than a quarter acre
2)Large-scale agriculture – pervious surface area greater than a quarter acre
3)Community gardens – pervious surface areas of 7,500 sq. ft. or more
4)Impervious surface and poor soil – impervious surface area of at least 5,000 sq. ft.
The inventory process involved the use of a variety of software tools. ArcView 3.3 was used to clip out developed areas and environmental zones; ArcGIS 8.3 was used to convert shapefiles to coverages and to clean regions; and ArcGIS 9.0 was used to create geodatabase files, join tables, union features, and for aerial analysis.
Results:
The research team developed several products as a result of their work. They conducted a baseline assessment of all the land currently being used for agricultural purposes within the city (Fig. 1). They also were able to assess land within the city boundaries that although not currently under agricultural use could serve agricultural purposes in the future (Fig. 2). In total they found that there are 289 locations within the city of Portland that could be used for agricultural purposes, which would allow the city to further its goals of developing a more sustainable community food system. Finally, the research team also created “site snapshots” in which they describe the plot size, agency of authority, zoning, district,and site accessibility, current condition and potential uses for five of the sites that they identified as being of potential agricultural use (Fig. 3).These sites were chosen in order to highlight the variability of lands that could be used for agriculture.
Relevance of Spatial Analysis for this Project: It would have been extremely difficult to conduct this research without the use of spatial analysis. The use of aerial photographs and GIS imagery allowed the researchers not only to see that there was a vacant lot, but to assess the condition of the lot as well as the uses of surrounding lots. This knowledge was very important in determining whether or not the land was suitable for agricultural purposes. One could potential conduct similar research assessing vacant space within the city boundaries, but in order to determine potential future uses for such plots additional information was needed.
Additional questions: It would be interesting to build on this data looking at some of the additional environmental factors that might impact suitability of agricultural use of a particular site. For example proximity to bus depots, land fills and other sources of potentially hazardous contaminants. GIS could be used to determine distance between agricultural lots and such sources.
FIGURE 1
FIGURE 2
FIGURE 3