[OSM-talk] Google Maps comparison

Andy Robinson Andy_J_Robinson at blueyonder.co.uk
Thu Oct 11 11:40:35 BST 2007


David Earl wrote:
>Sent: 11 October 2007 11:20 AM
>To: Richard George
>Cc: talk at openstreetmap.org
>Subject: Re: [OSM-talk] Google Maps comparison
>
>On 11/10/2007 10:58, Richard George wrote:
>> 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.
>
>Indeed. I have found numerous OSM errors while connecting to existing
>mapping in my area, and made many myself - obviously I've corrected the
>ones I have discovered. Often these are things like where a street name
>changes along its length, the second name is missing or the change is in
>the wrong place; but also place names - I corrected someone's Gamblingay
>to the correct Gamlingay (in two different contexts) earlier this week
>(don't mean to point fingers, I've made errors like this too).

We also have errors out in the real world too. In Birmingham most of the
street signs have the front end of the post code shown on them. Some of
these are plainly wrong (ie for a street with four signs one of them is
different). I also have examples where the name of the street is spelt or
laid out differently between signs at each end of the street (in some cases
with local paint-pot adjustments). A street that was originally two words
having become one single word for instance, which is correct??

If we want the definitive list/spelling we need access to the NSG (National
Street Gazetteer) but that alas is tightly controlled, not open to the
public and managed by the OS. On a local authority basis perhaps we can
obtain the list of adopted highways that they maintain. Because the LA has a
responsibility to maintain a street register for local property search
reasons maybe these lists are available to us, either voluntarily or via a
FOI request. Has anyone had any luck with such a request?


>
>Of course the biggest OSM error is that lots of streets are missing
>altogether. Often this is obvious because there's just a skeleton, but
>sometimes people have mapped 2/3 of streets spread evenly in a village
>(i.e. not the west half of the village, say, but an apparently random
>distribution which makes it look plausible).
>
>So long as we can't say in some way that we believe this is a complete
>area, I don't think it makes sense to talk about errors.

Indeed, which is why it's perhaps better to refer to these as "apparent
differences" rather than errors.

Cheers

Andy

Andy Robinson
Andy_J_Robinson at blueyonder.co.uk






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