I recently attended an excellent workshop on OpenStreetMap led by Jez Nicholson, and hosted by the Data Visualisation Brighton meetup. Entitled The map is not the territory, we looked at maps beyond being something that’s purely visual, and delved into the data behind them.
I’ve used OpenStreetMap many times before, but never done any editing. During the workshop we logged in and I suddenly found myself exploring a whole new world of information!
Lots more than meets the eye
The first thing that strikes me is the vast amout more detail available than you normally see. Of course, it isn’t possible to display everything on the browseable map, but that doesn’t mean it isn’t there. What you see when browsing a slippy map like the one on openstreetmap.org is just a subset deemed the most suitable for a general audience.
Everything is made up of shapes and tags
The format of OpenStreetMap data is relatively simple. Lines, points and polygons form the basic shapes from which all physical features are recorded. Then each of these items is has one or more tags identifying it.2 These tags have evolved dynmaically over time, no-one sat down at the beginning and worked out what all the tags were going to be. I find this rather fitting for the web. In the same way HTML has grown and adapted over time, the vocabulary of OpenStreetMap–and it’s usefulness–grows as more and more people contribute to it.
During the workshop I made a small edit, marking two bus stops as having a bench and/or shelter.3 A trivial change, but nice to come away having done something real and tangible.
What about Ordnance Survey & Google?
This organic growth is where OpenStreetMap differs from more “official” sources of mapping like Ordnance Survey. These organisations aim for very high consistency and accuracy, which they acheive at greater cost and a slower feedback cycle. Commercial providers have their own goals–Google maps and street view enhance their search offering.
These alternatives are fundamentally closed entities - you can’t alter the data, for good or bad. And both of these data sets come with terms and conditions dictating how you can use them.
There’s certainly room for both though. There are times when you want the assurance of thorough, unbiased surveying that’s gone into something like an OS map. You’d certainly take that sort of map out hiking, for example. But the existence of a global, freely-available rich dataset offers up so much potential and it’s exciting to see what can be done.