A few months ago I conducted a GIS analysis of the Angora fires in South Lake Tahoe impact to help LSNC’s Mother Lode office determine its response to that fire. Last night I began to wonder if a similar analysis might help legal aid organizations in southern California direct there response to the rash of wildfires currently burning their.

The aim of this post is to walk readers through mapping the impact of the fires in southern California on low-income residents of San Diego County in the Romona area. The analysis will be simple and only look at whether the fire has burned areas populated by low-income families and individuals. This approach has numerous short-comings but I think it could serve as an initial starting point of inquiry and, perhaps equally importantly, it can be completed in a short time frame (under two hours).

First, downloaded a shape file of current fires in North America. This data is a point feature class and can be accessed directly using this link.

Second, update (define) the geographic coordinate system of the feature class and its metadata in ArcCatalog. Need a refresher on updating geographic coordinate systems? How about metadata?

Third, the point features represent the centroid of a one kilometer raster cell so if we create a 0.5 kilometer buffer around the points the points we will get a rough approximation of the burn area. Since we don’t really need all the information associated with the buffer, dissolve the whole feature class (you might want to clip the buffered feature class to San Diego county before the dissolve if you have a slow computer). The resulting shp. file is an approximation of current fire areas in North America.

Fourth, use GIS Tools to extract SF3 P88. (Ratio of Income to Poverty Level) at the block group summary level. Use Excel or Access clip the dbf. fie to San Diego county (FIPS 073). Next, estimate the population eligible for LSC services in each block group. Using Excel, sum P088001 through P088010. This gives use the count of persons below 200% of FPL. Also, calculate the percentage of the population below FPL. Save the file as a dbf. (Tip: Remember that when you save the Excel document as a dbf. file you need to make sure any fields with decimal places are formated as “number” in Excel.)

Fifth, start ArcMap. Add the layer that you created in step 3, the USA basemap layer (it came with your copy of ArcGIS), and the dbf. file you created in step four. Download the census block group 2000 shp. file for San Diego county. Add the shp. file to the map.

Sixth, join the dbf. you created in step four to the census tract shp. file. The join will be based on the STFID field of the block group shape file and the SFID field of the dbf. file.

Seventh, examine the map to determine areas most likely in need of assistance. My initial concern would be with the northern parts of Romona due to the high concentrations of people below 200% of FPL. Providing immediate services to these area would likely be more efficient and have a higher impact due to the high concentrations of low-income persons.

In the end, I was hoping to complete this project in an hour and a half. It ended up taking me two hours but I still think that it was a fairly reasonable expenditure of time …. particularly because I could now examine the impact of the fires on all of San Diego county (at least in term of burn areas as off October 25, 2007). I hope this “walk through” helps give legal services practitioners an idea of “real world” GIS applications for the legal services community. Please feel free to contact the REP if you have any questions. (Post edited on 10/26/07 to correct buffer error).

Also, if your service area is includes parts of San Diego county and you would like specific maps please contact us. (No need to replicate work already done.)