[OSM-talk] Google Maps comparison

Richard George richard at phase.org
Thu Oct 11 10:58:19 BST 2007


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.
>
> As Cory has suggested, we need to make more of these findings..... I
feel a
> blog coming on.

Not to knock Dair's work, which is stunning, but I'd be wary about
announcing too many errors without some specific proof, lest it be seen
as crying wolf.

The "All of the above" error maps
(http://geo.topf.org/comparison/index.html?mt0=googlehybrid&mt1=tah&lon=-0.0968009&lat=50.9913397&z=17)
appears to show some errors with both data sets:

Google's routing of that part of Colwell Gardens that crosses Hospital
Villas is clearly off by their satellite data; OSM gets this right.
Google's vectors also overshoot the end of the shown roads in numerous
locations.

The routing and naming of that road are somewhat dubious on OSM.
http://www.google.com/search?hl=en&q=%22colwell+gardens%22+haywards+heath
suggests that this name/street exists. A similar search for '"Wellswood
Road", Haywards Heath' comes up effectively blank.

For this street to have the route now shown, a number of houses would
have to have been demolished since the aerial photo was taken; this is
possible but seems unlikely. The 'cap' roads shown in OSM are also
something of a conjecture - one can be seen to exist on the satellite
data but the other is a bit of a stretch.

This road, to be honest, looks like an OSM easter egg.

Neither map shows the road (which may be private) between St Edmund's
Road and Kent Road.

The roundabout (down by the postbox) at the bottom of these maps is
shown vastly too large by google, and entirely missing in OSM.



Having said all of the above, I know google's routing can be pretty
shoddy. At
http://geo.topf.org/comparison/index.html?mt0=googlehybrid&mt1=tah&lon=-0.1254791&lat=51.4558053&z=17,
for example, it will happily route a car from Lambert Road into
Strathleven & Madrell Roads, a journey which would involve, at various
times since I've lived there:

1) Smashing through an illuminated square white plastic bollard by the
"no motor vehicles" signs which were the original rat-run blocker.

2) Driving over the square section of raised kerb with one wheel in each
gutter-like cycle lane, and leaving gashes in said kerb, even if it
didn't take your exhaust off.

and most recently
3) driving through 3 very solid vertical metal bollards which replace
the repeatedly-smashed-off plastic one.

However, there's no evidence of any of these in the satellite photos.

HTH,
	Richard

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