Zoning Practice — February 2008

Ask the Author

Here are reader questions answered by Elisabeth Holler, author of the January 2008 Zoning Practice article "Monitoring Local Land Markets."

Question from David Nash, AICP, Planning Department, Fayetteville, NC:

I enjoyed the article regarding Land Supply Monitoring in the January 2008 issue of Zoning Practice. I do have several questions.

1. Let's suppose I set up my first GIS project to monitor land supply (using ArcGIS 9.2) for my local area. Let's suppose I use a current shapefile of land parcels for my county. (These parcels would have numerous attributes in a table.) Let's suppose I would use the attributes of the parcels to determine which are vacant and which are developed, and if developed, the type of land use for each parcel (i.e., residential, commercial, industrial, etc.). Let's suppose I add fields to the attribute table to enter the current number of housing units, by type (e.g., single-family detached, single-family attached, multifamily, and mobile homes). Then, say a year passes, and I want to reexamine the land supply. Should I go back and use the original shapefile and simply add new fields to the attribute table for the new number of housing units? Or, should I start from scratch with a new shapefile of new land parcels, and add new fields to the attribute table for the new number of housing units?

2. The scenario described in Question 1 assumes that I would use only a parcel shapefile. Another option would be to develop a point file that would have land-use and housing unit information and then join this point file to a parcel file, as of any given point in time. Do you see an advantage to developing a separate point file?

3. Have any jurisdictions used the Land Based Classification Standards (LBCS) as part of land supply monitoring? The LBCS was developed by APA, and it is available on the APA website (updated as of 8/18/03). It seems there might be some potential for using the LBCS as part of land supply monitoring.

Thank you for the opportunity to ask these questions. I look forward to seeing any answers you can provide.

Answer from author Elisabeth Holler:

Hello David,

You have hit on one of the most challenging parts of land market monitoring. Now that you have the data, how can you update it? Keeping the data fresh can take a substantial amount of time and expertise.

Regarding your first two questions, setting up the database depends on how the data will be used. Here in Orlando, we use a separate Oracle database to track land-use information by parcel, with the parcels geocoded to link to the GIS data. The "housing units" field is updated as units are built, so we do not have a historical record of what was on the parcel in previous years. We also enter new parcels into the database as subdivisions are platted. This process works well because data are summarized annually to identify overall growth patterns. We track this summarized data over time, rather than trying to track each individual parcel over time. In other situations, small projects with relatively infrequent data updates can be accommodated using attribute information connected to shapefiles. As projects get larger and more complex, it may help to link to a point file that is dedicated to a particular data-collection date, or to link to an entire database that is updated regularly.

Regarding your third question, I don't know of any jurisdictions that have used the Land Based Classification Standards, but this is certainly an idea worth pursuing. Gerrit and I would both be interested in hearing from people who have experience with this.