[OSM-newbies] Trust GPS or Yahoo aerial imagery?

[Rick Collins]

At 02:51 AM 10/9/2007, you wrote:
>Dave Clark wrote:
>
>Very very roughly, AIUI: the aerial imagery providers give a right to
>their customers (Yahoo included) to create derivative vector works.
>Yahoo has sublicensed this right to us. Their lawyers have checked
>this out and they're happy with it - and the OSM/Yahoo agreement has
>had sufficient publicity that, if the imagery providers had problems,
>you can bet we'd have heard about them by now.

Thanks for the info on the Yahoo images.  I figured that there must 
have been a good reason for the recommendation to appear on the Potlatch page.


>To answer the original question, though, trust your GPS over the
>imagery. The imagery may not always be rectified, whereas as long as
>your GPS has produced a good-quality track - i.e. no "concrete
>canyon" distortions - it should always be accurate.

I very much disagree with this idea.  Existing maps and images are 
not likely to be consistently off by a significant amount.  If they 
are, just find another source to make a comparison to.  I find it 
hard to believe that anyone who has used a GPS receiver much would 
think that they are consistently accurate.  I have never seen a GPS 
*not* produce errors.  There are any number of reasons for the 
inaccuracy of a GPS receiver including sun spot activity, cloud 
cover, limited sky view and low batteries, just to name a 
few.  Multipath is just one of many, many sources of uncorrectable error.