Personal musings on the authority of OpenStreetMap
Comments(6) There has been a lot of fairly excitable posting recently about the continuing rise of OpenStreetMap, and how it’s now being used in place of Google Maps, in particular since Google started charging for data. People have been talking about how “authoritative” crowd-sourced spatial data can be, and to be honest, I’ve found that the discussions seem to have missed the point a little bit. For me at least. So- here’s a few of my personal thoughts about OpenStreetMap and why it will be a while before I will consider it authoritative at least.
Firstly, a caveat. I love OpenStreetMap data and the whole ecosystem of “stuff” that has evolved around it. I contribute occasionally, though not as often as I’d like to. I’m pleased that it has forced the “traditional” data providers to reconsider what they offer, and perhaps to raise their game. I think it’s one of the main reasons why the idea of “open data” is so well known that even my Gran knows about it.
However, in the process of trying out WalkingPapers (my favourite addition to the OpenStreetMap ecosphere), I printed out the area around my house- in the centre of Lancaster. Not London, I admit, but still in the centre of a city. My road wasn’t on there. Read on, before you give up in disgust, saying “pah, you should just correct any errors you find”. How did I know my road was missing? There wasn’t an unfinished stub, with a note saying “I went home for my tea and I’ll finish this section tomorrow”, it was as if my road did not exist. I only knew my road was missing because I live there, and I have no readily available tools to help me judge the accuracy of an area that I am not familiar with. So, the idea that the end-user should correct any errors they find doesn’t really hold because you’re not always going to know that there’s an error!
I am aware that the traditional data providers do not produce totally error-free data. However, I would expect Ordnance Survey (for example) to have a workflow for their surveyors that doesn’t allow them to simply give up when they get bored or have to go home for their tea, or perhaps not survey a street because they don’t go down it very often. I can also go to the site and find published information on positional accuracy if I need it. I guess I’m equating “authority” with trust, or reliability, and the issue is less about what’s there, than what’s not there.
When OpenStreetMap is being used as a static base map, by which I mean a backdrop to the information your map is really about, this is less of an issue. But, if like me, you come from a discipline where maps are collections of data to be manipulated and analysed, then you need to be able to trust your data a little more, or at least have a quantitative understanding of what the error is likely to be.
I know that this is not an easy question to answer, and I know people are trying to figure out ways of answering it. I also know it’s not that important for a lot of people, but I would like to see a more nuanced debate- I think that would be better for OpenStreetMap in the end.
Well I guess some of the comparison tools using OS Locator data match what you’re asking for here (only in the UK obviously). Of those the most obviously accessible to newcomers would be to pick the ITO’s tile set as a background in Potlatch. Perhaps we should make that more obvious though.
Clearly that’s only been available since OS made these datasets open. Before that (and still in other parts of the world) we always follow a strict no copying stance. In general we provide “no readily available tools to help me judge the accuracy of an area that I am not familiar with” because that’s a form of copying. We mostly exist in an open data vacuum, with nothing to compare against without incurring derivation issues.
The UK community are still coming to terms with the availability of this data, and what it means for our mapping process. So in fact it’s still not widely accepted as a welcome contribution, for you to go comparing to OS datasets all the time and essentially copying in data from them. We’d actually still prefer it if people contributed their missing local streets based on their local knowledge, and using bing imagery or GPS readings to get positions. When it comes to the street you live on, surely you’re a pretty good authority on whether that exists!
Hi Harry, thanks stopping by. I’m not trying to criticise openstreetmap at all here- what I am trying to address is the excitable discussions that say it’s a solution to all the world’s problems, when it’s not. As I said, I’d hope a more nuanced debate would help matters.
But… your point about being the authority on data in your local area is exactly what worries me! Firstly, I didn’t mention copying data from Ordnance Survey at all and I don’t advocate that. What I said was that it’s only possible to fix problems if you know they are there, so yes I can digitise my own street, but someone using openstreetmap data who wasn’t intimately familiar with the area would not know there was a problem. Personally that means I feel like I can’t trust the data for purposes where there’s likely to be any sort of critical analysis of it. I would love to get to the point where it’s clear what’s missing so that it’s possible to use the data for more analytical functions rather than just as pretty but dumb base mapping.
Jo
Hi Jo and Harry
You mention some interesting points. As somebody who took some classes in remote sensing and who’s also digitised a bit on OSM, I’d suggest using good-quality satellite or airborne imagery (if available) as ground truth for mapping or map completeness assessment (the latter of course not automatically on a global scale).
I feel that this discussion is linked to a thread on this GI forum: http://geowebforum.ch/thread.php?threadID=1004 and which raises some further interesting points.
“I would expect Ordnance Survey (for example) to have a workflow for their surveyors that doesn’t allow them to simply give up when they get bored or have to go home for their tea”
They (OS Surveyors) get >paid< to be bored… and drink tea on the job.
The OSM is gaining more exposure and can be fixed (also vandalised) by anyone, OS do have a process but can take 6-18months to 'get' the fix.
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Jo, thanks for bringing back those memories of my days as an OS Surveyor and the workflow that left me taking non stop tide guage readings for 12 Hours!