Question exactly as in title.

asked 12 Apr '13, 17:14

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SK53 ♦
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edited 12 Apr '13, 17:15


This question was asked by a new contributor andrewj74 as a comment in changeset 15693142. As this seemed interesting and pertinent I thought I'd add it to OSM Help.

(12 Apr '13, 17:15) SK53 ♦

Although OSM was not designed for mapping history of objects there is considerable interest in doing so for a number of reasons:

  • Intrinsic interest. It is difficult to spend time surveying an area without wondering about quirks of it's geography which often have historical explanations.
  • Defensive mapping. POIs which have recently changed may be prone to being reverted if other editors are not aware of the change. Keeping the old values associated with the POI therefore provides an additional means of showing that something genuinely has changed.
  • Conflation with other sources. Many other sources of (open) data are not updated as frequently or rapidly as OSM. Being able to access recently used names or usages of POIs makes it much easier to make combined use of these disparate data sources.

This being said there is no firm consensus about how to tag this kind of information. For the immediate prior usage the most usual method is to prepend old_ to the relevant tags, such as old_amenity (161), old_shop (58), old_name (65 077), the numbers in brackets indicate number of times the tag has been used from taginfo. Much less widely used is old: as a namespace for the original tag, as in old:amenity or prepending dead_ to the value of key as in ['dead_pub'][2]. A very useful tag to associate with the change of use is [start_date][3], but this may need to be name-spaced to disambiguate between, say, a building, and its current use.

All of these work for one previous usage. I am not aware of anyone trying to tag multiple previous usages, but one can envisage a range of approaches, such as:

  • Just adding a numerical suffix to the old_xxx tags. So old_shop would be previous usage, old_shop2 the one before etc. This is a simple but maintenance gets complicated if usages are added out of sequence. Ideally this would be combined with start_date:old_shop and end_date:old_shop which would reduce this problem (although from personal experience it's extremely hard to find accurate values for these dates).
  • Using the suffix after old, so that shop=general, with old_shop=convenience and old2_amenity=pub would better represent a broader range of multiple uses. Again date range tags make it easier to interpret the data.
  • Date range namespaces to the key value, such as amenity:18970304:20121212=pub (roughly appropriate for the Golden Harp). This is more complicated, requires that we know the date ranges and is much less obvious for people editing and inspecting the data.

All these options really apply only to POIs with no changes in geography over time, but are widely applicable to shops, bars, pubs, restaurants etc.

There are a number of people interested in problems such as this one with a mailing list at Historical OSM.

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answered 12 Apr '13, 17:51

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SK53 ♦
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question asked: 12 Apr '13, 17:14

question was seen: 1,800 times

last updated: 12 Apr '13, 17:51

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