Buyers sometimes use Google Maps to find the longitude and latitude of the corners of parcels that they are considering purchasing. But exactly how accurate are those estimates?
In 2009, a Google representative said:
Google makes no claims as to the accuracy of the coordinates in Google Earth. These are provided for entertainment only and should not be used for any navigational or other purpose requiring any accuracy whatsoever.
Our imagery varies from sub-meter resolution in major cities to 15 meter resolution for most of the earth’s surface, with a global base resolution of 1KM. Since our database is constantly being updated, we cannot state a specific resolution for any geographic region.
Google acquires imagery from many different sources with many different file formats, projections and spectral characteristics. All imagery sources are fused into a single global database with a proprietary format that has been developed for the specific purpose of streaming to our client software.
So Google says that coordinates may only be accurate to 15 meters? Holy cow, that’s not so fabulous. Let’s see what the scientific researchers have to say . . .
Benker, Langford and Pavlis (2011) investigated accuracy in the Big Bend region of Texas. These academic researchers say:
A horizontal position accuracy of 2.64 m RMSEr was determined for the Google Earth terrain model with mean offset distance being 6.95 m. A vertical position accuracy of 1.63 m RMSEz with mean offset distance of 2.66 m was also calculated for the terrain model.
Mohammed, Ghazi, Mustafa (2013) examined Google Earth in the Khartoum State of the Sudan and say:
Root Mean Square Error (RMSE) was computed for horizontal coordinates and was found to be 1.59m. For height measurement RMSE was computed to be 1.7m.
Ubukawa1 (2013) evaluated Google Earth in 10 cities around the world and found:
The RMSE for the satellite imagery represented in Google Maps and Bing Maps was 8.2m and 7.9m respectively, and for OpenStreetMap it was 11.1m.
So to summarize, the scientists are saying that longitude and latitude could be off by several meters (yards). By extension, this presumably means that any property boundary lines you see in Google Maps could be off by several meters (yards).
What Does It All Mean?
Now I understand why I sometimes see property lines in Google going through the middle of driveways, roofs, golf courses, etc!
Given the possible inaccuracy you may find that coordinates are still useful, but only for some purposes and not for others.
Personally, I would use Google Maps longitude and latitude estimates in the following situations:
- Locating the land corners so that I can photograph the land for marketing purposes
- Finding approximate corners in order to decide whether to buy the land (except in the rare case where there seems to be some critical thing near the property line that makes a difference in my decision to buy or not buy, e.g., a neighbors house possibly encroaching)
- Identifying approximate corners so that I can look a few meters away in the dirt to find an actual survey marker in the ground
I would not use Google Maps for these purposes:
- Figuring out where to put up a fence along property boundaries
- Calculating setbacks to pour a permanent foundation to build a house
- Boundary disputes with a neighbor
The coordinates in Google Maps could be off by several meters (or yards). Google Maps is a great free resource when used wisely.