Accuracy of Google Maps

[RUSDIRUSLI]

I'm Rusdi, researcher from CARRS-Q, QUT. I 'm conducting data proccesing to identify of road geometric along my study area. I have two choices, either using my survey data by handheld GPS or using online map from Google Maps. My question is, how accurate google maps if my work is to identifiy alingment of the road (i.e. tangent and radius of road curve)?

[DanPatterson_Retired · Accepted solution]

i would use the survey data, we had reasonably good results using a vehicle mounted gps unit that could record position fairly densly... It has been some time but this might serve as a base for previous references.  Of course, gps technology has progressed substantially since that time. 

• Imran, M. Hassan, Y. and Patterson, D. 2006. GPS-GIS-Based Procedure for Tracking Vehicle Path on Highway Horizontal Alignments, Computer-Aided Civil and Infrastructure Engineering, 21 (2006), pp 383-394.

[RUSDIRUSLI]

Thanks Dan..When i go through my survey data, i found a few points not accurate when i seaching in google map.

[ChrisSmith7]

What type of device was used for GPS recording? Were the points post-processed/differentially corrected? What type of accuracy problems - minor deviations, or substantial outliers? If the latter, these can be cleaned-up fairly easily, but if it's the former, I would look into the collection and processing method.

[TedKowal]

Google Maps are only as accurate as the controls used to rectify the imagery.  In my experience, I have found Google Maps to be very accurate as well as way off in equal parts for the areas of my interest.  Personally, I would use the GPS over Google maps.  At least with the GPS, you may run across features that have known positional coordinate and then you can determine or even correct the GPS data.

I have re-rectified some of the Google Image and the results have been so warped and unusable.  So Google/Bing type  imagery is always my last choice to use.

[MichaelRobb]

Perhaps the google statement should answer your question enough?

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.

the answer to your question, 'how accurate' really depends on where and what the source was.  could range from 2meters to many meters... 

the decision is really then, how accurate do you NEED it to be.  I see legal boundaries cut through buildings on imagery for a reason... its not accurate enough.