tom chance's blog

Coverage of “points of interest” in OpenStreetMap is a point of pride for many mappers. Our maps have much richer detail than commercial competitors, they provide endless handy data for mashups, and as a consequence have been a big focus of mapping party efforts in London.

But should we really be so keen? I’m not so comfortable for two reasons.

First, how up-to-date is our data? I’ve recently re-surveyed my local area in minute detail and found several takeaways, shops and banks that have closed down or changed hands. I’ve also discovered that we have very poor coverage of cycle parking in Southwark following two years of massive expansion by the council.

How likely is it that these are being regularly checked and updated? I suspect “not very likely at all”, and have therefore decided to delete all my points of interest in my local area that I’m not confident anyone will update. I mostly deleted minor shops, especially those like hairdressers that change a lot and that aren’t very important to know about. I’ve left all the amenities like banks, post offices, cycle parking and pubs.

My second concern is that the completeness and up-to-dateness will vary according to the number of active and nutty OpenStreetMappers in the area. And that tends to translate to affluent areas.

In their useful paper on the “completeness” of OpenStreetMap, Muki Haklay and Claire Ellul issue this rather stark warning:

“The large number of contributors for applications such as OSM or Google Map Maker might convey the false impression that [they] represent a real democratisation of geographical information collection, whereas the reality is that these many voices are coming from the more affluent and naturally empowered sections of society. This cacophony is likely to be silencing the voices of the marginalised and excluded even further.”

As I have auto-traced buildings in deprived parts of Southwark from Ordnance Survey StreetView tiles and sporadic re-surveying, I have noticed the very patchy and thin coverage of points of interest in those areas. Probably half the churches and schools are marked with nodes (no ways describing sites and building, though I’ve tried to draw them in) whilst the rest are missing entirely; occasionally there is a smattering of takeaways and convenience stores.

A comparison of allotments with an open dataset from the Greater London Authority reveals a similar pattern (previewed above). Most of those we have missed are in deprived areas. I’ll be revealing more work on completing our allotment coverage soon, courtesy of some help from friends and contacts in various local/regional government departments.

Muki and Claire suggest public agencies should step in to improve coverage in deprived areas, but that requires a high level of committment to OSM from those agencies. Currently we are in the very early stages on this front in the UK.

Given all of this, I would be interested to hear what other OpenStreetMap contributors and followers think. Should we bother with minor points of interest like hairdressers and takeaways until public agencies step in? Is it better to leave them out to avoid a database full of out-of-date information that only increases inequalities of coverage?