Skunked tags
A skunked term is one whose meaning has evolved over time, making it difficult for a reader to know what was originally meant and making it difficult for a writer to use without causing confusion or offense. Likewise, a skunked tag is one that has been redefined over time, making it difficult for a data consumer to know whether a given occurrence of the tag was meant to follow the old or new definition.
A tag does not automatically become skunked just because a few mappers misuse it, but it can become skunked gradually with prolonged misuse by a community of prolific mappers.
Causes
Tags that arise due to any tags you like are particularly vulnerable to skunking. A word in English may have multiple valid meanings, and some forms of iterative refinement lead to collisions between multiple top-level feature tags. Compounding the matter, raw tags are often coined or interpreted by mappers who have an imperfect command of the British English dialect. Preset names may mislead some users into inadvertently using the wrong tag. Some tags are skunked by mappers tagging for the renderer.
Disadvantages
A data consumer cannot easily predict which definition of a tag was used when a mapper added it to a feature. Even if the data consumer can analyze the feature's history, the intent can become obscured when the feature is split or merged. If the data consumer cannot come up with a heuristic to distinguish the two definitions, it may have to ignore the tag entirely.
Prevention
The best prevention is to discuss a tag widely soon after you coin it. The feature proposal process is one mechanism for raising awareness about an intended definition, but an approval is no guarantee that a tag's definition and actual usage will remain stable in the long term. Seek the participation of relevant stakeholders in any discussion, including both mappers who are enthusiastic about applying the tag and developers who might potentially consume it.
Even though this is a global project that welcomes new tagging ideas from everyone, it is prudent to consult with fluent or native English speakers in tagging discussions, since the tag will likely be interpreted as British English unless there is a good reason to do otherwise.
Mitigation
Depending on the severity of the situation, it may be possible to salvage the tag to have a consistent meaning by relegating the other meaning to a new tag. Sometimes it is possible to clean up a skunked tag by reviewing each occurrence manually using a tool such as MapRoulette. But if the skunking happened long ago and there are too many occurrences to review manually, it may be necessary to split out a new tag for both definitions, deprecating the original tag as a historic artifact. This may be an unsatisfying outcome if the original tag had an elegant name.
Examples
This is a list of some of the skunked tags that have caused the most controversy in OpenStreetMap over the years. Inclusion in this list does not necessarily mean that the tag should be deprecated, just that mappers and data consumers should exercise caution when imparting too much meaning from these tags. In some cases like sport=football problem was solved by deprecating tags.
- crossing=uncontrolled – Originally approved to mean marked with zebra stripes, despite the British English definition; widely interpreted as being unmarked in English-speaking regions but marked in non-English-speaking regions; documented as de facto marked once crossing=unmarked was approved
- crossing=zebra – Originally used on UK-style zebra crossings; replaced by crossing=uncontrolled crossing_ref=zebra in a vote; subsequently used as shorthand for all marked crossings outside the UK
- highway=service – Inadvertently conflated with a preset for dedicated golf cart paths (in combination with golf=cartpath) that was adopted by prolific golf mappers; possibly led to an accident involving a delivery truck [1]; eventually fixed by deconflating presets
- highway=trunk – Every country came up with diverging, sometimes conflicting definitions; most countries eventually adopted a connectivity-based definition, but Germany and the U.S. eventually equated it to expressways; routers adopted this performance-based definition, even after the U.S. split out expressway=yes and adopted a connectivity-based definition
- network=ncn/rcn/lcn – Originally used for the UK's National Cycle Network, Regional Cycle Network, and London Cycle Network; later redefined as any national, regional, or local cycle network, respectively; U.S. mappers coined cycle_network=* to distinguish the many individual networks at these levels
- service=driveway – Widely understood to refer to prototypical residential driveways and service roads with a similar function, but very often applied more broadly by speakers of some American English dialects, as well as languages that lack a precise term for driveways
- shop=deli – Originally defined as a delicatessen that specializes in fine gourmet foods; in the U.S., usually applied instead to the much better-known concept of an American-style deli or deli counter; in Japan, often applied to shops that sell sushi, tofu, etc. to go
- sport=football – Variously interpreted as either association football or American football by both mappers and data consumers [2]; eventually deprecated in favor of sport=soccer and sport=american_football, respectively
- access=permit - originally intended to be used for ways where permit is required but available to general public (so you need to do something in advance), some defined it as being ordinarily granted to general public. As of 2023 it is widely used for all kinds of ways requiring permit, including ones like "only for workers of a steel mill" or "residents only"
- access=private - originally intended for ways where access is restricted. As of 2023 it is widely for ways that are "private" in any sense. This usage duplicates access=permissive as well as ownership=private.
- shop=boutique - intended to be subtype of clothing shop, in many places this tag is widely, but wrongly used to tag shops unrelated to clothing as in French speaking areas "boutique" is commonly part of a shop name and one of meaning of word "boutique" in English is a shop not restricted to being a clothing shop
- amenity=pharmacy – Originally referred to a standalone pharmacy that only sells pharmaceuticals, but commonly applied to drugstores (shop=chemist) that contain pharmacy counters; eventually applied to the pharmacy counters within drugstores and supermarkets
- healthcare=pharmacy is duplicate of amenity=pharmacy and inherits the same problem
- highway=road – Originally approved as a generic catch-all for any kind of road, regardless of its physical construction or functional classification, but later broadened to include both roads and paths