Hackney: “Complete” on OpenStreetMap

ITO‘s OSM Analysis table is updated daily, showing the number of roads in each district/borough in the UK that are in the OS Locator* dataset that are missing in OpenStreetMap. There is an accompanying choropleth map (you need to login to seet it) showing coverage across the UK. Currently southern England and Scotland’s central belt are looking pretty good, while Wales and parts of northern England still have quite some way to go.

As well as the map and summary table, ITO produce a map showing the approximate location of each missing (or misspelled) road, as a rectangular bounding box. This makes finding the missing roads quite easy. Groundwork is needed to check signposts and confirm the names. Often, discrepancies arise simply from OpenStreetMap not having apostrophes for the street name, and the Ordnance Survey having them, or vice versa. The signposts normally provide the definitive answer, but in quite a few cases, the sign at one end of the street will have an apostrophe and the other end will be missing it – or the names attached to houses will differ from the nearby street signs.

Hackney was around 94% complete a few weeks ago, with around 80 errors flagged up. It’s a small borough (in size, if not population) so I reckoned it was possible to bike around all 80 locations in a day – with a suitable route that would hopefully be a good answer to the Travelling Salesman Problem.

In the end, I managed it in a couple of afternoons. I found quite quickly that in most cases, the street was already in OpenStreetMap but just misnamed or unnamed. In around 5-10% of cases, the Ordnance Survey was wrong, and street signs on the ground suggested either that OSM was correct, or that both sources was wrong. As the OS was in general right, I only stopped to note where this wasn’t the case – so, I was able to cover a lot of ground quite quickly. I still ended up having to cycle nearly 100km within a borough that is roughly 4-5km across.

Perhaps the most interesting part of the exercise is it allowed me to visit all parts of the borough, including places I had never been to before despite having lived there for several years. I discovered that Stoke Newington Church Road is indeed massively gentrified out of all proportion to the surrounding area. I found unexpected gems like The Mothers Square (no apostrophe) and that Hackney Downs is quite a pleasant park. I also found the huge Pembury Estate. This was where one of the Ordnance Survey’s mistakes was – the streets were named in the wrong order. Perhaps the original surveyor didn’t like to hang around.

Of course no map can ever be 100% “complete”. Even with a perfect match to OS Locator, the latter may be out of date, or be missing roads due to missed records. The map may be “complete” in terms of roads but other detail still needs to be added.

Anyway Hackney is now 100% complete with respect to OS Locator, making it the 12th such district in the UK. Another 400-odd to go…

* OS Locator is one of the products in Ordnance Survey’s OpenData release.