Problems and possibilities with ward boundaries

Being actively involved in my local branch of the Green Party means I’ve spent a lot of time wandering around carrying a map of a local ward.

Almost nobody seems to know which ward they are in, often because the names are a bit abstract (e.g. “The Lane” in Peckham, which I presume is because “Rye Lane” runs through the middle) or because almost nobody would say they live in the area described (e.g. “Peckham Rye”, which has Peckham Rye Common and Park in the middle and includes areas normally thought to be part of East Dulwich and Nunhead).

Since the Ordnance Survey published open data, including political boundaries, it’s been possible to put this information into OpenStreetMap. I’ve finally bothered to start doing this for Southwark – you can see the results on this nice ITO map.

Unfortunately the default map on the OpenStreetMap homepage draws the names of the wards along the rather nice dotted boundaries, displacing actual road names and leaving junctions that could easily confuse the user. Here are three examples:

You’ll notice I’ve added “ward” to the end of the names to try and help, but it’s not much of a solution. Three different proposals have been put forward on the OpenStreetMap bug tracker (a dedicated map, hide them, make them less bold).

A simple solution to the problem above would be to remove the names; a more sophisticated solution would be to give road names priority, change the text colour to the purple of the boundary lines, and hope Mapnik allows us to offset the labels so you can have the two ward names either side of the line).

It’s a bit of a shame that they create a mess because they’re useful data to include in OpenStreetMap (much like trees, which I’ve asked for a solution to).

For example, the holy grail of software to help us canvass voters would be to connect the electoral register to the OSM database of houses, allowing us to visualise and manage information on voting intentions and canvasser visits by ward on a nice map.

Another useful application could be Nominatim, which could tell you the political boundaries that any chosen OSM-mapped home, business, park or set of co-ordinates lies within.

For now I just need to finish getting all those Southwark boundaries into the database…

Data quality

One other quick point. The London Borough of Southwark boundary was already in the database, but it’s not very well mapped.

It’s really important to know if a boundary runs down the middle of the road, so that homes on one side belong to one borough and homes on the other side to another borough; or whether the boundary is offset away from the road, usually down back gardens, so that all homes on both sides are in the same borough.

Fellow OpenStreetMappers should be careful to put the boundary in exactly the right position, ideally sharing nodes/ways with the actual roads where the boundary goes down the middle so it’s precise and won’t go wrong if somebody adjusts the road position.