|boundary = historic|
|A historic administrative boundary (use judiciously)|
|Used on these elements|
|Status: in use|
|Tools for this tag|
This tag has been used on boundary relations for a variety of reasons that can all be described as historical boundaries. Depending on the reason a historical boundary was included in the map, it may now be eligible for deletion and migration to OpenHistoricalMap. If the reason is unclear, consult with other mappers before deleting it.
Boundaries of historical significance
Many uses of this tag represent former administrative boundaries that have been abolished long ago but continue to be attested on the ground or in everyday usage into the present day. Examples include some of the geographic townships of Ontario, Canada. boundary=traditional and boundary=ceremonial have also been used for this purpose.
Some historic districts are best modeled as site relations instead of boundary relations. For example, in the United States, many historic districts on the National Register of Historic Places are described as a boundary for convenience but are formally defined as a collection of contributing properties, excluding any "intrusions".
Recently abolished boundaries
Instead of this tag, consider using a more explicit lifecycle prefix, i.e., was:boundary=administrative or disused:boundary=administrative. Eventually, the boundary should be deleted once there's no longer a risk of recreation based on outdated imagery or an external source. Adding end_date=* helps mappers determine when it is safe to delete the boundary.
Some mappers have mapped long-defunct boundaries from historical sources. However, purely historical data is outside the scope of OpenStreetMap; consider contributing this data to OpenHistoricalMap instead.
As of June 2022, about half of all boundary=historic admin_level=* boundaries globally come from an import of electoral districts of the 1911 census of Ireland (source=Census of Ireland 1911 online).  This is not to be confused with an import of census boundaries from the 2015 census (ref:IE:census2015=*).
How to map
The boundary=historic tag is used on ways . It may also (or instead) be used on a relation grouping several ways. admin_level=1 to 10 may be used in addition to further clarify the relationship to present-day administrative boundaries. Consider using note=* to explain the reason for applying this tag.