Proposal to change the Key:start_date wiki page


I would like to motivate a change in the description of the Key:start_date page,

start_date=* can be used to indicate the date the feature opened or construction of the feature finished (i.e. started to exist as feature)


start_date=* can be used to indicate the date the feature began to exist most often the date the feature opened or construction of the feature finished.

This date should correspond to the feature as it exists today, neither to previous states nor to its predecessors.

The start_date does not apply only to the main descriptive tag (e.g. highway= or railway=) but to the entire feature, i.e. its geometry, its main tag and all other descriptive tags excluding identifier (as wikidata,wikipedia…) and source tags (i.e. all descriptive tags are valid on this given date, start_date should not conflict with these).

1-2 The first two sentences seems like a detail but the original one may introduce some confusion. In a number of cases this seems to be interpreted as “the main tag started to exist as feature” e.g. it started to exist as a church. However by reading the Good practice I see that we are not supposed to map neither historic features nor objects if they do not exist currently, the date given should therefore be the date of the feature as it exists today. Historical mapping remains possible but falls under dedicated projects such as OpenHistoricalMap.
Here are some examples if I follow the current practice “the main tag started to exist as a feature” vs “the date of the feature as it exists today”:

  • Mons (Be) train station started to exist as a feature its main element being building=train_station in 1874… however these first two stations no longer exist so the date of the feature as it exists today will be 2024-2025 (it is not finished yet).
  • Church of Saint-Étienne in Lille (Fr) started to exist as a feature its main elements being amenity=place_of_worship+building=church in the 11th century… however the current church is originally a chapel of a religious congregation built in 1610, destroyed by fire on October 8, 1740 and rebuilt in 1748 in Baroque style and it only became a parish church under its current name in 1796 following the destruction of the first church located 300-400m from there.

In a complex case such as this, we can use a start_date:note or start_date:cause to give details accompanied if possible by a source.
In the case of modified buildings, there is always the possibility of using building:part to date each part of the building but the feature with building= should always include the date it began to exist as it currently stands.

3 For the last sentence, the majority of start_dates do not have a prefix (e.g. name:start_date, ref:start_date) which in itself is not problematic if this start_date is for the date the feature began to exist as it currently stands . Likewise we must be able to assume that at the given start_date all the descriptive tags (excluding sources and identifiers) were true. If I take the example of Charleroi-Central railway station, the start_date is 1843-07-30, however the name “Charleroi-Central” only appeared in 2022 and there is little chance that the station was accessible to wheelchairs in the 19th century just as the SNCB/NMBS operator has only existed since 1926, here the start_date conflicts with the other tags of the feature.
We may include a date for the main tag (this could however be a historic feature and therefore not have its place here) but as this only concerns a single tag it should use the appropriate form main_tag:start_date (e.g. highway:start_date or building:start_date) without causing conflict with the other tags in the feature.


  • on renderers: none.
  • for users: no feature modification necessary, this mainly targets objects with a complex history which most of the time do not have a start_date or already have a correct start_date (a simple building=yes with start_date=1750 is not affected by this change).

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