Thursday, October 15, 2009

Google Maps – Sleuthing Changes in Data Sources and Geocoding Methods

Google has caused a bit of a stir by dropping Tele Atlas as their US data provider and switching to their own, self-managed dataset. Google has caught some flack in the blogosphere for being less than transparent about their data sources and providing nothing even resembling metadata. Users must discover for themselves what and where is new. The road centerlines have changed, public parkland and campus maps have been added, and in some areas parcel lines are displayed. Also, Google has added a quick link for reporting user suggestions for error corrections and updates.

Looking at my neighborhood it appears that Google is using a mix of parcel addresses and route geocoding to locate addresses. In my area if you search for a correct parcel address the marker is placed within the parcel boundary, as in the first map example. There is an error here in Google Maps. The road marked Gardenwood Ln is actually my unnamed driveway and Gardenwood Ln is the private road to the east. If you search for a correct Gardenwood Ln address the marker is correctly placed within the proper parcel (the second map). However, if you search for a Gardenwood address which is not in the parcel data, the route geocoding places the marker on the incorrect Gardenwood Ln (i.e. my driveway on the third map).

The Gardenwood Ln error seems to have come from the US Census Tiger Data, suggesting Google is using TIGER data as a source, at least for Albemarle. (OpenStreetMap, which uses TIGER data has the same error.) Albemarle County GDS and the VGIN RCL datasets both have the correct Gardenwood Ln. Presumably, Google is using Albemarle GDS parcel data for parcel lines and addresses. I have reported the error to Google but have not yet heard back. Is anyone else finding parcel lines in their locality? Is parcel information available? Comments welcome.

1 comment:

  1. I've recently found that parcel lines for the City of Richmond and Henrico County are available.