Thursday 15 November 2012

St Nicholas gate

Beverley, in East Yorkshire, is a market town, which like many others, feels like it is all jammed into a small space. It has expanded into two adjoining villages, Molescroft and Woodmansey but the space within Beverley is still at a premium. The town has had industry in the past, especially a large tannery and I expect the good people of the town are now probably happier not to have the place as the smell was awful. The site became a museum for a while but for some years it has lain as rubble strewn waste ground. Now a new housing development has started and the first houses are complete.

I have been biding my time, waiting for access before I surveyed the roads. When the latest OS Locator comparisons highlighted three of the roads as missing from OSM I decided it must be time to take a look. One road, Simmonds Close, is quite conventional, but the other two are a little different. The front door of these houses face onto a short pedestrian road with a service road behind each one with garages and access to the rear of the houses. I wandered up each road, GPS in hand and chatted to the builders who were finishing some of the houses off, then went on my way.

When I got home I discovered that OS Locator has labelled the service roads as the missing roads (Hamilton Walk and Dickinson Walk). I suspect the clue is the name guys, the walking bits are the named roads, not the service roads.

There was a good view of Beverley Minster from the end of one road.

Tuesday 13 November 2012

OS Opendata in OSM

Prompted by a comment from Socks, I have looked at some of the GB regions where Ordnance Survey road names don't match the names in OSM. The OS Opendata names on roads are provided by OS StreetView and a textual version is provided by OS Locator. ITO World and Musical Chairs both use OS Locator to create a graphical tool to help people identify where the OS & OSM names for roads differ.

Sometimes the name OS has for a road does not match the name displayed on a name board for the road. OSM uses the name from the name board. To help with the processing of anomalies the wrong, OS name can be added as a not:name tag. The occurrence of the not:name tag is a useful indicator to the origin of the names in OSM. If the names closely match the OS list then the OS names may have been used and the actual names may not have been surveyed. In this way the errors in the OS datasets find their way in to OSM.

One possibility is that mappers in an area may not use the not:name tag. They may not like it or maybe they don't know about it. If they survey their road names and don't use the erroneous OS names then these anomalies should show up in any comparison.

I looked at some of the data about OS Locator and threw some data into a list for the most complete 250 authorities. ( I lost the will to live after 250.) You can see the list at If you click the headings it will sort that column, allowing you to see where how each authority compare.

Friday 9 November 2012

Short cuts

The latest version of OS Locator open data has been released. Musical Chairs and ITOWorld both published updated information. There are five new names in Hull and seventeen in East Yorkshire all to be visited, checked and then updated.

Of course there is a short cut. I could just use the names OS supply and update the roads in OSM without checking. That would be easy, I could do it from home without spending any time out in the cold and the city and county would quickly look complete again. I could get most of this from the OS StreetView, copying the road names from the tiles overlaid in the editors. Would that be a good idea?

I have checked some of the areas that have slowly had the number of anomalies whittled away and it seems that about 3½ to 4% of the roads named get a not:name tag to show that what is shown on the ground is not the name OS think it is. So if I just copied the OS names  without checking them I would be introducing about a 4% error into the names in OSM.

Looking at a few places where the names have suddenly had a huge reduction in the list of anomalies it seems that the checking may not have been done. Sheffield has a not:name ration of 0.5%, Penwith has a ratio of 0.9%. Taunton Dean has no not:names at all. It is possible that this ratio is right, but it seems unlikely. I hope that people do manage to sort this out over time, but a road with a name is not likely to have its name resurveyed, so I suspect most of these will persist.

I like the OS Locator data and I'm grateful to the people who process it and make it available to mappers. It is a great way to find out the roads that have been added or changed recently (thanks OS) but please use OS (or any other data) sceptically, it is not perfect, it needs checking. Short cuts are only useful if they preserve the quality.