|Identifier from the United States Board on Geographic Names|
|Used on these elements|
|Status: de facto|
|Tools for this tag|
A GNIS feature ID is a permanent, unique identifier for a feature in the Geographic Names Information Service (GNIS) database. GNIS is the U.S. federal government's authoritative gazetteer. It contains an entry for each named place or point of interest recognized by the U.S. Board on Geographic Names within U.S. territory, based on submissions from federal, state, and local government agencies as well as from the general public through The National Map Corps.
GNIS feature IDs are an ANSI national standard and INCITS industry standard. They are used throughout the U.S. federal government, having officially superseded the previous system of FIPS codes in 2008. 
Most uses of this tag and its synonyms were introduced as part of imports of U.S. federal government data, especially from GNIS itself. Unlike other imported tags such as gnis:created=* and gnis:import_uuid=*, gnis:feature_id=* is meaningful beyond the import. In fact, some mappers actively add gnis:feature_id=* to features to cite a verifiable source for the POI's existence or its name.
When converting a GNIS POI to a landuse or building area, copy the gnis:feature_id=* tag to the new area to preserve the link to external details.
If a local POI has moved, you can use look up the feature ID to find its current coordinates.
Some local POIs may no longer correspond to a real-world facility, because there is no automated process for synchronizing OSM with the GNIS database after the initial import in 2009. Moreover, since October 2014, the USGS no longer actively updates local POIs in GNIS apart from changes submitted through The National Map Corps. If a real-world POI has been demolished, delete the POI from OSM including the gnis:feature_id=* tag.
If a facility has closed or been repurposed but the building still stands, the GNIS feature ID remains valid, so it is acceptable (but less important) to leave the gnis:feature_id=* tag in place. (Some old schools, firehouses, and covered bridges have landed on national or state registers of historic buildings, which you can indicate using heritage=* tags.)
Note that updates to GNIS-imported features in OSM will not automatically be reflected in GNIS, in part because OSM's license is incompatible with the requirement that all U.S. federal government works be released into the public domain. If you want your updates to be reflected in GNIS, you will need to crosspost your changes to The National Map Corps via their online editor. (Only crosspost changes you author yourself; do not indiscriminately copy ODbL-licensed data over to that public domain project.)
Finding a feature ID
Use the GNIS domestic query form to find the entry for a particular place or local POI. A replacement search tool is available but incomplete and not as easily linkable.  For populated places, another interim search tool is also available with similar limitations.
Alternatively, you can search for parks in Wikidata. Most GNIS park features are included in Wikidata and tagged with a P590 (GNIS ID) statement. You can also indicate the Wikidata identifier itself using the wikidata=* key.
|gnis:id=*||some of these came from a 2007 import of populated places, some came from NHD imports|
|tiger:PLACENS=*||from a 2009 import of TIGER places|
|NHD:GNIS_ID=*||NHD imports in some states|
|nhd:gnis_id=*||NHD imports in some states|
|ref:gnis=*||Encouraged by some JOSM relation templates|
- ref:nrhp=*, another U.S.-specific external identifier, used in conjunction with the National Register of Historic Places
- Dynamic Sophox map of missing or untagged GNIS features