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

[Rick Collins]

At 11:19 AM 10/9/2007, you wrote:
>To be fair, the "consistent" error in question was only one track.  I
>assumed that all the tracks in the region were consistently skewed in
>relation to Yahoo.
>
>I'm a lone mapper (at least I was the last time I checked) I don't have
>a dozen other people criss-crossing my region that I can use to estimate
>my GPS's drift - I have to trust my GPS over the images because those
>are the only two data sets I have available to me.

You can use the USGS data sets.  I use a free program called 
USAPhotoMaps which is an excellent way to access the USGS data via 
terraserver.com.  It allows you to import GPX data sets as tracks and 
view them overlaid on either photo data or topo maps.  At least if 
you are in the USA this is an option.  Are you somewhere else?

As for other sources, I don't think that comparing your data to 
Google or any other online source of map/photo info would be a 
violation of copyright.  It would be an issue if you used their data 
to generate your data.  But I expect using their images to verify 
your data would be acceptable.


>For you guys doing detail work in well tracked areas, it may be a
>different story. But for those of us who are laying down the initial
>tracks on a completely blank canvas, we  don't have the option of
>trusting outside imagery over our own data.
>
>
>
>"Maps are not meant to be precision lookup thingies, they are meant to
>be big overviews, as good as possible."
>
>Boy is THAT true.  I use a 3 year old maps on my PocketPC version of
>TomTom - the maps for virtually every housing allotment built in the
>past 15 years is skewed to the point that automatic navigation is
>completely impossible.  But, if I view the maps directly, the streets
>appear OK relative to eachother: Turn left into the allotment, turn
>right on HomeOwner Lane, and another right on Colorful-Imagery Way.


I would say that these particular maps are crap, not a condemnation 
of all maps.  I have a Mapopolis program with fairly accurate maps 
and the USGS data seems to agree with my GPS data once you take out 
the wanderings of the GPS.  On the other hand, the road maps in my 
Meridian GPS receiver tend to be skewed, although not consistently in 
one direction or distance.