The Stages of Completeness

25 06 2008

First we must think about what it is important for a map to have, a complete map will obviously contain all of those important features. The features necessary may differ from user to user though, tourists may be interested in the location of landmarks whereas those travelling into work every day need accurate road maps with all turn restrictions and road names etc. In general I think named accurate roads are the most important feature so a lot of my analysis will be to do with the length of roads present in OpenStreetMap. That is not to say that POIs such as restaurants, post boxes etc are not important it is just that for these to be placed well we need a complete mapped road network. With this is mind I have developed a way in which we can follow the progress of the completeness of an area on OSM, using a stage system.

  • Preliminary stage – GPS tracks gathered or area has yahoo imagery.

  • Stage 1 – Nodes and ways mapped onto OSM using GPS track or aerial imagery.

  • Stage 2 – All roads named and roughly categorised

  • Stage 3 – Map good enough for satellite navigation. All one-way streets, and restrictions tagged along with accurate street categorisation.

  • Stage 4 – All POIs (i.e. post boxes, bus stops, pubs, restaurants, supermarkets etc.) tagged.

These stages may or may not occur in sequential order and each stage can be quoted complete in terms of percentages. For example we might say that London is 100% complete for Preliminary and stages 1 and 2, but only 60% stage 3 complete and 20% stage 4 complete. The hard question is how do we accurately measure these percentages. It is easy for a human to tell that the map of London below is more complete than that of Madeira with its limited amount of roads and dead ends but its a lot harder for a computer.

Central London, a complete map Madeira, an incomplete map
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2 responses

25 06 2008
Tom

One other consideration is – for whom is the map complete?

For a pedestrian, aspects of stage 3 will be unimportant (one way roads, for example) whilst certain POIs and in particular areas like parks will be of huge importance.

Likewise for a cyclist in London, a further stage would include data on the London Cycle Network with additional relevant POIs.

Another way of making your question more subjective – where do I want to go? We have increasingly detailed data in the London Borough of Sutton, which is great if you want to visit a friend or go to the Secombe Theatre, or if you also include much of West London in your daily life, but not so hot if you’re looking to go over to Streatham Common or down into parts of Surrey.

25 06 2008
Ed Johnson

That was another point in my research which I thought I had added to the blog. Its certainly correct that the user is of utmost importance. I think I’m going to need different stage criteria for different users.

I like your final paragraph too, although I need a way to turn these subjective questions into concrete answers. The dream is to have a rating or a grade of completeness which can be easily quoted if for example some asks so how complete is the map in Streatham?

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