[Talk-GB] The curious case of USRN 20602512

Nick nick at foresters.org
Fri Jul 10 11:45:57 UTC 2020

Hi Mark

Brilliant comment - "because the people who are most likely to spot 
errors - members of the general public with local knowledge - tend not 
to have easy access to the data". Now we need the evidence (errors) 
collated centrally (OSM?).

On 10/07/2020 11:27, Mark Goodge wrote:
> Apologies for the long read, but this may be interesting to some folk. 
> This follows on from my earlier response to Kai Michael Poppe about 
> "Fairfield Road" in Ealing.
> On 04/07/2020 12:02, I wrote:
>> To find the USRN of the path, you need to use the lookup tables 
>> supplied by OS. Doing that, we find that the associated USRN is 
>> 20602512.
>> Now, there's no open data source which will directly tell you the 
>> name of a USRN (at least, not until we start putting them into OSM). 
>> The long way of doing so is to find the matching LineString in OS 
>> OpenMap Local, and see what name it has there.
>> However, it can be done directly via a non-open source. If you go to 
>> https://www.findmystreet.co.uk/map and zoom in on the location, then 
>> click the street to bring up the USRN details, it will give the name 
>> (and also confirm that the USRN from the OS lookup table is correct). 
>> Or use the search box and search for USRN 20602512.
>>  From an OSM point of view, that would normally be a dead end. Even 
>> if you can view the information on a non-open source, you can't 
>> incorporate it into OSM. However, in this case, we already have an 
>> abbreviated name from an open source. So all we are learning from the 
>> closed source is the full text of the abbreviation. Whether that 
>> makes it acceptable to include the full name into OSM is a matter of 
>> debate. I'll leave that decision up to others, but, for reference, 
>> the name of the street is Fairfield Road.
> I've been doing a bit more research in this, as it piqued my interest. 
> And the results are a little surprising.
> For a start, USRN 20602512 doesn't match Fairfield Road in OS LocalMap 
> Open. In fact, there's no Fairfield Road anywhere near there in OSLMO. 
> Matching the coordinates indicates that, as far as OS is concerned, 
> it's a part of Southdown Avenue. That's not particularly unusual, 
> access roads off named streets often don't have a name of their own, 
> they're either completely unnamed or share the name of their parent 
> street.
> However, I did wonder whether this might just be a limitation on OS 
> Open Data, and whether MasterMap might actually include the name. 
> That's not reusable in OSM, of course, but it might help point to an 
> open source that does contain it.
> But it seems that even MasterMap doesn't have that name. You can check 
> that by looking at Ealing's online GIS website:
> http://maps.ealing.gov.uk/Webreports/Planning/Planning.html
> This is a planning application map, but it's just a window into their 
> GIS system and you can turn off the planning layers. Anyway, zoom all 
> the way in to the street in question - I can't give you a persistent 
> link, but it's just above the LA boundary in the bottom middle of the 
> map - and... it still has no name. At the highest zoom level, this is 
> MasterMap, and every named object has its name displayed. But there's 
> no name here.
> Google, also, knows nothing of a Fairfield Road here. Using the Maps 
> API to query the coordinates of USRN 20602512, we either get Southdown 
> Avenue, again, or Boston Gardens, which is the postal address of 
> buildings facing Boston Road. You can see that name on the road sign 
> via Google Streetview:
> https://goo.gl/maps/KGLbRC75mQw43PCV6
> So, it seems that Fairfield Gardens isn't known to either OS or 
> Google. It is shown (in abbreviated form) on streetmap.co.uk, but at 
> that zoom level, in London, that's based on the Bartholomew A-Z maps 
> rather than OS.
> Given that, we can't include the name "Fairfield Road" in OSM as it's 
> only available from non-open sources. But even those non-open sources 
> don't agree on the name. That seems to me to lead to two possibilities:
> 1. It doesn't exist at all. It's just a map trap designed to catch out 
> unwary copyright infringers. That's certainly a possibility, and A-Z 
> maps are known to use those. But that doesn't explain its presence in 
> the USRN database.
> 2. The USRN name is wrong, but that error has propagated to the A-Z maps.
> Personally, I think that the second option is the most likely. And, if 
> so, it wouldn't be the only error in USRN. One of the things I had to 
> deal with a few years ago, in my capacity as a district councillor, 
> was a country lane in my ward that had the wrong name assigned to it 
> in USRN. After a bit of investigation, we concluded that it had simply 
> been a transcription error back in the late 90s when the local 
> gazetteer was first digitised, but it had gone unnoticed for a couple 
> of decades simply because the wrong name never appeared anywhere in 
> public until it eventually cropped up on a planning application. 
> Getting the name corrected wasn't an easy task, because of the length 
> of time it had been wrongly recorded, but we did eventually manage to 
> get it sorted out and the correct, historic name of the lane assigned 
> to the USRN.
> But that's not the only one. The USRNs for where I grew up, out in the 
> middle of the countryside in West Suffolk, are listed as either 
> "Poultry Road" or "Sedge Fen" in the USRN database. You can see that 
> by looking at https://www.findmystreet.co.uk/map and searching for 
> 14610160. But, in reality, the road name is "Sedgefen Road", and this 
> is correctly shown by MasterMap, Google and OS LocalMap Open.
> This is, of course, one of the problems with proprietary data. It can 
> be difficult to spot errors, because the people who are most likely to 
> spot errors - members of the general public with local knowledge - 
> tend not to have easy access to the data.
> So this is a bit of a warning, really, for the open mapping community. 
> Although the open data release of USRN ids and coordinates is welcome, 
> don't be tempted to look up street names on the street list published, 
> with a restrictive licence, on https://www.findmystreet.co.uk and then 
> copy them to our own data. Because it simply isn't reliable enough as 
> a guide to actual usage, even if it is what the "official" name of the 
> road may be. Stick to OS Open Data and local knowledge.
> Mark
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