Tuesday, 21 July 2015

OSM Retail Survey: Part-1

According to the Valuation Office Agency (the organisation which assesses business rates in England), there were 528,000 retail premises in England in 2012. This includes shops, banks, post offices,  cafés, restaurants, and take away food outlets, It doesn't include pubs or wine bars. It includes kiosks, some service providers (e.g. hairdressing salons), but it doesn't include filling stations.

To get a comparable figure from the OSM database we need to extract a mix of tags: most shops, some amenities, and some offices. So far I have found 142,803 features in England that fit the VOA categories of retail property (27% of the expected total). The shortfall across England is 385,000 retail premises that VOA have counted, but which I can't find in the OSM database.

The VOA statistics are broken down by local authority, so it is straightforward to compare OSM coverage at local authority level.

In notoriously well-mapped areas such as Nottingham and the neighbouring authorities of Broxtowe and Erewash the number of retail premises recorded in OSM is close to the number of retail premises reported by the VOA (Nottingham = 2,996 in OSM, 3,340 from VOA). In Tendring (Essex), the OSM tally is 95% of the VOA figure. In Oxford, and Cambridge it is almost 80% of the VOA figure.

I'm sure I must be missing some retail properties that I should be counting, and counting some that I shouldn't. Overall, though, these well-mapped areas suggest that I must be quite close to capturing what I hope to capture.

  • In 34 local authorities I reckon that more than half of retail premises are recorded in OSM,
  • In 24 local authorities less than one in ten of retail premises is recorded in OSM. 
  • The lowest levels of retail coverage are in Burnley, Castle Point, Doncaster, Eastbourne and St Helens.

Regionally, intense mapping around Nottingham means that the average coverage of shops in the East Midlands is relatively high (though not as high as the average across Inner London).

The lowest levels of coverage tend to be in larger northern towns and cities. Picking a few at random, I found less than one in ten shops recorded in Bolton, Doncaster, Rochdale, South Tyneside, and Sunderland. In the south, towns like Basildon and Luton do not fare much better.

Coverage of shops across rural counties is close to the national average.  The most complete rural areas border intensively mapped cities (Nottingham, Oxford, Cambridge). The least complete rural areas are widely scattered.

It doesn't really work this way, but imagine for a moment that the community collaborated to raise more areas to the standard achieved by leading examples such as Nottingham, Oxford and Cambridge. The obvious approach would be to prioritise areas that could be completed relatively easily, and the quickest wins would be where there is only a small shortfall between the number of retail premises reported by VOA and the number of retail premises recorded in OSM.

  • The smallest shortfalls between the VOA statistics and OSM content include authorities like Rutland (140), Maldon (176), Eden (201), Redditch (261), and Wokingham (269).

More generally, mapping of shops involves wandering around recording them. Comparing two authorities with a similar shortfall, it stands to reason that a more compact area would need less effort than the larger one:

  • There are just four authorities where coverage is already in the top decile, and size in the bottom decile, and all are inner London Boroughs – Camden, Westminster, Islington and the City of London.
  • There are nine more authorities that rank among the smallest 20% by area, and highest 20% by coverage. All are outside London. In addition to Oxford and Cambridge they include Cheltenham, Norwich, Redditch, Southampton, Tamworth, Woking and Worcester

By contrast, the local authority where I live covers a large area, has a low population density, and the proportion of retail properties recorded in OSM is below average. There is a long way to go before it ranks among the most thoroughly mapped. Random searching for shops could take a long time, so I need some way to prioritise.

To be continued....


joost said...

I did a quick check for bakeries in the city I work, Antwerp, Belgium. There's a good datasource available through the statistical website of the city (which by a complete coincidence, I happen to be one of the managers of). So I thought about comparing at the most detailed geographical level, a census tract (statistical sector). But the city wide comparison says enough, I'm afraid. The official count for the whole city is 294, OSM has 37.

gom1 said...

Thank you Joost, this is exactly the kind of comparison I wanted to encourage. I hope local mappers will now add bakers.