Monday, 27 July 2015

OSM Retail Survey: Part-11

The occupants of a retail premise will change over time, and as a result we should expect retail data in OSM to continually evolve as well.

Most of the retail data within OSM is less than 5 years old, so the chances are that the bulk of this is still more-or-less current. Around 5% of the data is 5-years old, and 2% is 6 years old. A growing proportion of this older data could now be inaccurate, but across the country it is likely that the proportion of data that is out-of-date will only represent a few percent of the total.

In some places (e.g. Islington, Leeds, and Sheffield), more than 10% of shops were added to the database over five years ago. In parts of Kent more than 30% of the shops were added more than five years ago. So there may be a case for some local reviews of older data, to update anything that has changed since it was last recorded.

In most locations, though, the current priority will still be to add missing data, then later work towards greater accuracy.

In the longer term, that picture is likely to change. In the last 12 months 28,000 retail properties in England have been edited. That's 5% of retail properties that have either been added to OSM, or updated. Some of the changes in OSM data over the last year will have been to correct a spelling, or to adapt tagging, and will not have involved a re-survey. But we can't easily measure how much has been fully updated. So for now, let's be optimistic, and assume that every edit brings that particular shop up to date.

If nothing changed on the ground, then at this rate it will take more than a decade to approach complete coverage of retail. But the situation on the ground does change. In 2014 the average length of a retail lease was less than nine years, and almost half of retail leases were for less than four years. Retail leases used to be for a longer period, and because of peaks in construction activity in 1990 and 2000 an unusually high number of 25-year, and 15-year leases are currently due for renewal.

 Not all retail property is leased, leases will sometimes be renewed without change of occupant, and some might carry forward for generations. So I don't know what proportion of OSM high street data we should expect to change over a year. If only 5% changes then current levels of editing activity are sufficient to maintain existing data, and gradually close the gap of missing data. But if we assume 10% of existing retail premises change over a year then the current rate at which OSM retail data is being edited will not be enough to deliver and maintain complete and accurate data on all retail properties in England.

Nationally, perhaps something like 7,000-14,000 entries on the database should be updated each year. Around where I live, the rate of change looks closer to 10% per year, rather than 5%, so I'm guessing a decent estimate of the national picture will be closer to the higher figure.

As database volumes rise there will be more to maintain. If contributors concentrate on adding missing retail properties, then by the time coverage reaches about 50%, the existing data will be going out of date as fast as new data is being added. If contributors concentrate on maintaining what has already been added, then they will have no time to add the missing 50% of retail properties. Either way, for the foreseeable future, there is going to be a lot of retail data that is either missing from OSM, or incorrect on OSM.

 If we can wait long enough, other factors might help. A decline in the number of retail premises would also accelerate progress towards 100% coverage, and the chart shows the effect of a 2% reduction in the number of retail properties each year. Even if this is factored in, reaching a worthwhile level of retail cover still looks like a slow process. Too slow.

It is not only individual shops that change. Retail business models also evolve, and over the long term we should expect this to affect the choice of tags. Some formats which once were common on the high street no longer exist (ironmongers into hardware, then homeware). A traditional grocery, or a video rental shop is now unusual.

On the other hand, perhaps candle shops are returning to the high street (“shop=candle”), and e-cigarettes are a recent arrival. The data on chains of mobile phone shops may be an example of how this process continues. Currently these chains are tagged with a mix of “mobile_phone” (95%), and “electronics” (5%). Perhaps contributors are adapting their tagging, in recognition that an established speciality has now matured, and the offer is starting to evolve as retailers extend into adjacent markets.

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