Implementing Lot/Land Maps in San Diego

Did you ever wonder why VERY VERY FEW real estate sites have really good lot/land real estate maps? This blog entry seeks to explain the problems and to give you some ideas on how you might solve them.

Recently we implemented real estate maps with Lot/Land data pulled from the MLS RETS server. This had been a troublesome set of maps to create, so I decided to share some of my ideas with our colleagues on this.

Just so you know what I'm talking about, I'll show you a piece of one of the details of one of my current Encinitas and Carlsbad lot/land map:

Sample section of Carlsbad and Encinitas Lot/Land Map

Just a note on the above map....The pushpins are color-coded by price for the lot, and the number on the pushpin tells you the approximate number of acres (rounded up or down). Click here to see the Carlsbad and Encinitas lot/land map for yourself.

The reason that you don't see many (if any) lot/land real estate maps is because it is hard to get a reference point for the maps. In the case of detached homes or condos, there is a postal mailing address. This is usually provided by the MLS in their IDX or IDX/RETS data feeds. Once you have the address, you can use Google, Yahoo, or one of the commercial geocoding vendors (e.g., Melissa Data, ESRI) to turn the address into a latitude/longitude coordinate pair that can then be mapped. In the case of Yahoo and Google, you can even geocode the address in real time when the map is created so that you don't have to store the address.

In the case of lot/land property, there is often NO ADDRESS with which to geocode. Or, if there is an address, it is a fake address (e.g., 0 Garden Way) just so there is a place holder. In actuality, it's just a lot at the end of the street, and if you pass that fake address to the geocoding provider, it will often fail to geocode the address because the address isn't a valid one in the USPS address database.

The ONLY real unique qualifier for Lot/Land data is the Assessor's Parcel Number. Once you have the Assessor's Parcel Number, you can figure out where the property is located. I am not suggesting that geocoding all of these parcels will be easy - it will NOT be. Fortunately, the number of lots for sale is very, very small compared to the number of homes (attached/detached), so the total workload isn't huge. But, make no mistake, if you tackle this job, it is a commitment.

The next problem that you are likely to run into is the difficulty of acquiring the APNs for the IDX data. Unfortunately, the IDX and IDX/RETS feeds are determined by the local MLS. If the local MLS does not want to include the Assessor Parcel Number in the feed, then it won't go in the feed, AND THAT'S TRUE EVEN IF THE DATA IS NON-CONFIDENTIAL. In the case of the San Diego MLS (which is really quite good in giving a wide variety of data), they don't yet supply the APN number in the IDX or IDX/RETS data feeds for any of their datasets, including land. This is a bit strange in one regard since one of their fields is named "Tax Parcel for RETS." Hopefully that means that they will be supplying the data eventually.

Anyway, one can easily create a custom query within the MLS and pull the MLS Number and the Assessor Parcel Number for all of the active listings. Then, with that information, you can update your database for your map with the APNs. NOTE: Don't just use the downloaded data as your primary data thinking that you can bypass the IDX feed; if you do, you're likely to display a listing which is No-Internet-Display, and then the MLS will come knocking at your door. However, downloading the list allows you to supplement the IDX or IDX/RETS data feed.

Then you can easily write a query against your data to show you which APNs are missing latitude/longitude coordinate pairs. Then, as painstaking as it is, you can go look up the APNs and see where they are located, and, if you use GoogleEarth, you can get the latitude/longitude coordinates. Plug those into the database, and you can then add those lot/land parcels to your map display!

If you have any questions about our map implementation, you should send me an email and I'll forward it to my husband John (who does all this technical work). If you know of another good lot/land map, please drop us a line; we'd like to see it. Margaret