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

[Mark Huizer]

Rick Collins wrote:
> Maybe you guys should take a step back and look at what you are 
> saying.  You have one person with a $200-$400 GPS receiver recording 
> a track which then is hand edited to add to an open source map.  This 
> track disagrees with aerial imagery that companies have spent 
> millions or even billions of $$$ to collect, process and 
> provide.  Now you are thinking of telling a distributor of that data, 
> based on your single track of collected data, that they need to 
> "correct" their data.
> 
> Do you really think they are going to take you seriously?  Perhaps 
> you are thinking of the Yahoo imagery as if it were a collaborative 
> effort like OSM?

Maybe you might also take a step back and look at what you are saying :-)

But anyway. The quality of imagery isn't constant all over the world. Different companies make the images, they are bought by the Googles, Yahoos, Mapquests, etc... Making pictures from an airplane requires callibration, of course, requiring ground markers at known locations to callibrate the imagery to right coordinates. And some assumptions about detoriation of your pictures, your speed, etc.

There is no reason why a decent GPS with good reception can't be more accurate than aerial imagery, especially in between those marker points. A decent GPS, given good reception and enough time to measure (or enough measurements by various GPS'es etc) can easily get within 5 meter accuracy, or better. Google Maps has been shown to be a multitude of that distance of in various places, enough examples of e.g. geocachers looking up caches in google maps only to find that the given coordinates are actually 30, 40 or more meters away on the other side of roads/water/whatever. Maps are not meant to be precision lookup thingies, they are meant to be big overviews, as good as possible. GPS are more capable of giving you exact coordinates. In short: there is a time and a place for each of them.


And no, they are not 'going to take you seriously'. But maybe not because what you tell them is nonsense, but because it is not gaining them anything to follow up to your remarks.

I'd say that given the fact that the way OSM data is collected by people going around mapping stuff (amongst other ways of getting data), and that that way of working is a conscious decision, I don't see reason why you would have to put the things the way you are doing. As far as the 'correcting' is concerned: the maps of OSM, Yahoo, Google, etc are not perfect. What's so bad about trying to notify people of mistakes you find? Even if they have a different model from OSM?

So far my 2 eurocent, perhaps the OSM powers that be have yet another opinion, but I'd say the newbie list is not the right place for discussing the project's goals

Mark