[OSM-talk] Google Maps comparison

[Dair Grant]

Andy Robinson wrote:

>That's really, really nice work. I was quite struck by the sheer
>number of differences. I've seen plenty in my area but as yet haven't
>looked closely enough to see just how many. Your results suggesting 9
>per square kilometre of urban area would make an astounding number
>for the whole country if it ramps linearly.

It is hard to know how to interpret them - it's quite 
overpowering to see an entire town covered in push-pins, as it's 
hard to convey significance.

For example, the non-existent stub opposite Lucas Grange is 
"wrong" - but is not really important 
<http://tinyurl.com/39bypx>. On the other hand, these two roads 
have a line of trees separating them so are completely separate 
for road traffic <http://tinyurl.com/3ycero>.

They're both wrong, but the latter is more likely to cause 
problems (if you are routed through there, you'll have to turn back).


The approach I took was just to ask myself if the OSM map was a 
better representation of reality - if it was, it got flagged.

It would be interesting to find some towns of a similar size in 
different areas of the UK/different countries, and verify them 
to the same degree.

After a couple of those you would start to get a feel for how 
(a)typical this case is.


There are no doubt still some mistakes in the OSM map, and some 
things flagged as errors are really a judgement call.

E.g., the Lucas Grange stub is actually someone's drive; these 
seem to be included at random on Google Maps, even though 
they're not part of the road network. You can see similar 
choices with little parking stubs like this:

     <http://www.flickr.com/photos/dair/1437518682/>

I always capture these, but Google/Yahoo include some but not others.

My guess is these kind of things are deliberately 
included/excluded to give the map a "fingerprint", as there 
doesn't seem to be any real consistency for when they're captured.


-dair
___________________________________________________
dair at refnum.com    http://www.deathvalleycycle.com/