Geocoding and GPS 101: How to do it now, and how it ought to be done

Jeff Jones, Research Fellow

I was having a conversation with a long time customer last week when the subject of geocoding came up. What is it? How does it work? Why doesn't it always work? The usual questions. And I have had the conversation and ensuing discussion many times before, too – while teaching a WinTOTAL class section on mapping, or when one of my customers calls to ask why his new construction properties are mapped in the wrong state.

What exactly is geocoding? Geocoding is the process of converting a named location (i.e. a street address) into unique latitude and longitude coordinates. Geocoding isn't an exact science...well, actually that is not true. It is a very exact science as it relates to its ability to locate a property on an exact and unique point on the earth. No two properties will ever have the same latitude and longitude and the accuracy can be down to the millimeter although it's usually within several feet.

The part of geocoding that is not exact is the database. New construction and vacant land usually have no recorded street address (at least not one that has made it into the public records). The street address is required by the map servers in order to assign the latitude/longitude coordinates and this is where the system fails. It is really no different than a recent sale not showing up in public records or MLS.

Here's a very simplified explanation of what must occur in order for geocoding to work properly.

1. A property must be assigned a street address by a local municipality. This usually happens when the property is developed or built upon.
2. That street address is recorded as a matter of public record. This can take days, weeks or months depending on the backlog.
3. The mapping software provider such as Microsoft, Rand/McNally, Garmin or DeLorme must "discover" this addition to public records. This discovery process usually takes place at predetermined intervals and some providers are better at staying current than others.
4. The mapping provider's servers must be updated to be able to resolve the new property's street address into lat/long coordinates.

So as you can see, the responsibility for accurate geocoding results falls on two parties, local governments and mapping software providers. Therein lies the problem. If either fail to do their job in a timely manner, the system fails. As an example, I live in a neighborhood of 122 "newer" homes that began development in 2003. My entire street (not just my specific address), did not show up in Microsoft MapPoint until the 2007 version!

So what is an appraiser to do when working with new construction, vacant land or simply properties that have not made their way through the system? One option, albeit not a very good one, is to just let the software "guess" where the properties are. Then simply zoom and pan around the map manually moving comp balloons until the locations are correct. Although this is at best cumbersome and time consuming, from my experience, it is actually the solution most appraisers utilize.

There is a better way and the basic functionality is already built in to WinTOTAL. By using a simple, inexpensive handheld GPS (Global Positioning System) device, the appraiser can completely bypass the geocoding system and enter known lat/long coordinates directly into WinTOTAL. GPS devices provide the user lat/long information by communicating with 3 three or more of the 24 GPS satellites that revolve around the earth. These positions can be marked, named and saved for use later. By providing the mapping software with the information it needs from the beginning, the street address to latitude/longitude conversion process is eliminated, thereby all but guaranteeing an accurate mapping result.

Here is what you do:

1. Buy an inexpensive (approx $150.00) GPS receiver with the capability to store "waypoints" (lat/long coordinates).
2. For those properties that are questionable as to their "geocodeablity," mark the coordinates while on–site and assign the waypoint a brief description in the GPS device.
3. Mark additional properties as required giving each a description.
4. When completing the appraisal report and while in the Maps Powerview, remove the property address and enter the GPS coordinates of each questionable property in the appropriate fields before downloading the location map.
5. The software backend utilizes GPS lat/long coordinates instead of street address when querying the map server and determining property locations.
6. The correct property locations are displayed on location map.

Obviously, this is a predominately a manual process – from marking the waypoint in the GPS receiver to transcribing the data into WinTOTAL. I am convinced this process can be greatly improved upon. My ideas are still very young and will require a lot fine tuning but here's what I am thinking.

What about a small stand–alone application the user could install on their GPS–enabled PDA or smartphone? Or could we possibly integrate this tool into the next generation Pocket TOTAL? Something that would allow users to record and name GPS coordinates while in the field and transfer those coordinates into their WinTOTAL report using an "Import From GPS Wizard" in the Maps Powerview. This would eliminate the tedious process of manually transcribing the data from the GPS unit (and thereby eliminate the high possibly of error resulting and properties being placed inaccurately).

It is true that most appraisers do not use this function now but the reason is they simply do not know it is possible. When I demonstrate the current process during classes, the response is overwhelming. You can almost see the light bulb go off – especially for those appraisers who specialize in vacant land and new construction.

Now, go to the GPS project integration page