Key:start_date
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 start_date
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Date when feature opened or the construction of the feature finished. 
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| Group: properties |
| Used on these elements |
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| Status: de facto |
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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).
 | A feature should only have a start date after it really started (i.e. do not add predicted dates). For a feature not already started consider to use opening_date=* |
Formatting
Exact dates
Dates use the ISO 8601-01 system, which is based on the Gregorian calendar. Be aware that for exact dates there are differences of up to 11 days between the Gregorian and Julian calendars and that different countries switched to the Gregorian calendar over a 400 year period.
Examples:
- start_date=2010 ; where the year is known, but no more
- start_date=0897 (for 897 CE)
- start_date=1848-07 ; where the year and month are known
- start_date=2010-03-31 ; for where the full date is known, using the format yyyy-mm-dd
Caution: ISO8601 uses the format yyyy-mm-dd, not the model of mm-dd-yyyy or dd-mm-yyyy
Approximations
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Often a date will not be known exactly. In which case some of the following can be used:
- start_date=~1855 (some time around 1855)
- start_date=1860s (during the 1860s (i.e 1860 → 1869 inclusive))
- start_date=~1940s (probably during the 1940s)
- start_date=480 BC (for something that happened in that year)
- start_date=before 1855 (during 1854 or before)
- start_date=before 1910-01-20 (before a specific date - possibly when a photo was taken)
- start_date=after 1823 (after 1 January 1823 - possibly based on the year in which a map was produced)
- start_date=C18 (during the 18th century)
- start_date=mid C14 (some time during the middle of the 14th century)
- start_date=late 1920s
- start_date=~C13 (probably in the 13th century)
- start_date=1914..1918 indicates some time during WW1.
- start_date=2008-08-08..2008-08-24 indicates some time during the Beijing Olympics.
- start_date=mid C17..late C17
- start_date=j:1918-01-31 (a date using the Julian calendar, equivalent to 1918-02-13 in the Gregorian calendar)
- start_date=jd:2455511 (Using the Julian day system, equivalent to 2010-11-10 in the Gregorian calendar)
- Muslim calendar?
- Notes
'1800s' means the years 1800-1809, not 1800-1899. Prefixes of 'early ', 'mid ', 'late ', 'before ' or 'after ' to indicate those things.
Avoid seasons. For example 'summer 1998' as these vary between the hemispheres. Consider using '1998-05..1998-08' for summer in the northern hemisphere.
BCE can be used in place of BC. AD is assumed where BC is not used but optionally be included.
Avoid multiple entries, for example 2010-08-01;2010-08-19 without providing at least an explanation in a note.
Marking a civilization, period and era
You can also add information by setting the following keys (no need to restrict them to features with a historic=*):
- historic:civilization=* please see the documentation which values are suggested
- historic:period=* please see the documentation which values are suggested
- historic:era=* please see the documentation which values are suggested
Appendix
Some values drawn from a review of Taginfo: start_date, on 2010-11-10 show severe heterogeneity.
End date and alternatives
end_date=* is sometimes used to mark end of existence/validity of features. Without additional precautions the use of end_date is considered a trolltag and the use of it is likely to break existing routing and rendering software if used without namespace prefixes on main tags. For alternatives see Comparison of life cycle concepts.
Open Historical Map uses end_date extensively.
Possible Tagging Mistakes
See also
- construction_date=* - date of then construction has been finished
- opening_date=* - date of an approximated opening in the future
- end_date=* - date of when a feature is planned to go out of use, or when it went out of service.
- year_of_construction=* - date or date range, during which the object was in construction.
- taginfo '_date' search
- Comparison of life cycle concepts
- OSM-4D for ideas about a viewer showing features in 3D extended over time.
External links
Maps showing start_date
Modules for working with start_date values
- JavaScript module for parsing values
- JavaScript module for formatting as human readable string
- JavaScript module for generating regular expressions queries (e.g. for Overpass API)