Monday, February 17, 2014

"Local Food Practices and Growing Potential: Mapping the Case of Philadelphia" 

In an era of increasing globalization coupled simultaneously with an increase in the global population overall (increasing demand, translating into higher prices), local food systems are an increasingly viable alternative to the globalized food system. The authors in this article use the city of Philadelphia, Pennsylvania as a case study to explore the socio-spatial structure of the current local food system, integrating remote sensing and GIS techniques to estimate land potential for urban food production. 

The authors argue that "a fundamental principle for the promotion of sustainable food systems is the understanding of pathways between production and consumption of food" (1253). They first identify the relevant components of the local food system in Philadelphia, focusing on urban and regional local food production, distribution, and outlets for local foods within the city. Using 2000 Census data, the authors illustrate how the structure of urban local food systems in Philadelphia is influenced by socioeconomic characteristics and their variation. For example, the authors find that 53% of the farmers' markets are located in census tracts with median incomes above $30,000. 18% of the farmers' markets or just 7 locations total, are located in the lowest-income neighborhoods with median incomes below $18,000; however, over half of these locations (4) are strategically placed adjacent to important city institutions, such as City Hall. 

In total, the authors geocoded 94 urban and regional farms producing food for the city's 38 farmers markets. The authors then developed a network analysis to evaluate the distance traveled by farmers selling in Philadelphia's farmers markets using the "closest facility" tool in the ArcGIS Network Analyst extension. The model simulated 152 routes representing the path food travels from farms to farmers markets in Philadelphia. Using ArcGIS "Point Distance" tool, the actual travel distance required between farms and farmers markets is on average 10 miles greater than a straight line distance. The overall average travel distance is 61 miles, with most farms traveling between 20 and 70 miles to deliver their products to farmers markets. 

Finally, the authors implemented geographical analysis techniques to calculate the potential for urban food production. Combining remote sensing and GIS techniques, the authors estaimted the potential of yard space that is bare of vegetated, and then integrated those areas with parcel and zoning data to "better refine an estimate of the amount of vegetated and bare soil in residential areas" (1257). Using a series of selections, clip and erase operations on ESRI Desktop ARCGIS 10, the authors overlayed the zoning data with the city parcels, focusing exclusively on residential areas. 

The results of the NDVI analysis are shown above, with 46% of the city's 91,237 acres bare or vegetated. Residential areas occupy 34,326 acres and 44% of those acres have building structures on their parcels. This data suggests that residential and community farming practices might be feasible to implement in Philadelphia, and would shorten the average travel distance of food from farms to farmers markets. 

Kremer, Peleg & DeLiberty, Tracy. (2011). Local food practices and growing potential: Mapping the case of Philadelphia. Applied Geography, 31 (4), 1252-1261.


  1. I found it very interesting that in the first diagram that the community gardens (the yellow circles) were clustered around areas with black or dark grey shading (very low income families) and as you went into the areas with higher incomes, the community gardens would dissipate. Not only that but it seems that any sort or urban gardening over all is few and far between in areas with higher incomes. It would make sense since those with a higher disposable income would be able to make the commute to a farmer's market or have the means to get the products offered there. Would implementing community gardens in low income areas within the city help families get access to nutritional fruits and vegetables?

  2. Could the authors have taken this a step farther and identified an estimate of how much food could be produced within the city and how much of the cities food supply this could fulfill? That would be a very interesting next step, although potentially difficult to estimate accurately.

  3. Thanks for your comments. Vallery, I don't think the authors specifically discuss whether it would help families get better access to nutritious food, but I think what they do try to do is demonstrate that the land within the city limits of Philadelphia is there and available to be used for more community gardening. Therefore, this implies that food would travel a shorter distance to low income communities if more community gardening was in place. So I think that Alec's comment is right on - the next step in this project would be to identify an estimate of how much food could be produced with the 46% of residential area that is bare or vegetated.