The Freedom to Tag

In OSM, we neither have nor want strict rules. We have got where we are now precisely because we did not waste time trying to come up with rules, especially for tagging. There’s anecdotal evidence of competing crowdsourced “geo” projects that spent precious years haggling about the correct ontology to use, while OSM boldly started out with about three types of features (the “class” tag of yore could be one of “highway”, “railway”, or “waterway”).

Not a week goes by without some discussion on a forum or mailing list ending in a lament about the lack of strict tagging rules. Data users hope to be able to find out that the feature they’re looking for will, if it exists, be tagged exactly so and so. Junior mappers want to know how exactly to tag certain objects. Experienced mappers despair at others changing their hard work according to some wiki “vote” that attracted 15 participants out of tens of thousands.

This the first of four big issues that I believe we’ll have to tackle somehow.

Not only was it tagging freedom that got us where we are now; we are also an international project with diverse communities and there is no reason why everyone in the world should tag things the same. Just because a guy in Germany cannot tag a pub without adding a building outline, roof structure, and the opening times of the premises and, separately, the kitchen, doesn’t mean that this makes sense for everybody.

But still the issue remains, and a lot of valuable time is wasted between mappers discussing the merits of one tagging scheme or the other. Sometimes, edit wars ensue which then bind even more resources in mediation.

Meanwhile, editor writers and bot programmers gain all the power – it is, in effect, them who decide which presets are available and which tags will be used for each, and which additional information is requested of the user. Some editors even complain if the mapper tags something that is not in line with whatever the author of that editor thought to make sense. And some people write bots that “auto-correct” what they see as a mistake.

This is a continuing source of friction. Our data is more valuable and easier to use if it is easy to interpret; mappers could often benefit from that as well. But tagging freedom, and the lack of a “central tagging command” structure, have brought us where we are. In contrast to other systems like Google Map Maker, our mappers are not just worker ants expected to mind-numbingly fill in the blanks on a form; they can be creative agents deciding what gets mapped and how. Out of despair some people even call for a “tagging czar” who would make a decision whenever the community doesn’t arrive at one. This doesn’t look like a good solution to me but it illustrates the gravity of the situation.

The project changes, and the bold and autonomous mappers of the first few years (who often had a whole city to themselves) are in decline; we have more people who actually want to be told what to do. But with many of the experienced people in our project being from that bold generation and not wanting to create rules for others, we end up with rules being made by people with strange ideas whose main spare time activity seems to be rule-making rather than mapping, and voted on by people who might not grasp the consequences.

Over the years, lots of ideas have been voiced or even tried out. It is somewhat customary to propose new tags on the Wiki and discuss them there, but that process attracts precious little participants. Some users seem to view proposing new features as a kind of sport; the classic Skyhook proposal was a humorous response to that. There’s a school that suggests a more top-down approach, perhaps best illustrated by David Earl’s “Tag Central” model presented at State of the Map 2010 (slides, video); others favour the heuristic approach first sketched by Richard Fairhurst under the working title “floaty cloud Tagwatch on steroids” and best embodied today by Jochen Topf’s TagInfo. Lots of halfway houses are possible; much as any state-of-the-art shopping site tells you “other people like you have bought this”, one could envisage an editor that says “your friends tend to use the tag X for this”.

This is not about tags alone; it is about the mapping style in general. How much detail do we add? Do we use separate geometries for parallel features? Do we use points, lines, or areas for certain features? All that generally sails under “freedom to tag”: a freedom that many would like to see limited by rules of some kind; an issue where we’ll have to find a good way forward that works for us all.

(The ideas in this article were first posted by me to the talk mailing list in December, under the subject “Looking forward”. I have edited them and elaborated a bit for the blog.)