|source = PGS|
|Prototype Global Shoreline: coastline data from the US National Geospatial-Intelligence Agency|
|Used on these elements|
|Status: In use|
|Tools for this tag|
PGS is short for "Prototype Global Shoreline" created by the US National Geospatial-Intelligence Agency. Many natural=coastline ways in OpenStreetMap were derived from the PGS dataset around 2006. As of 2016, approximately 25% of natural=coastline ways have source=PGS. 
Although this tag is mainly about ways, it also appears on many nodes. Years ago it was typical for imports to put metadata tags, such as source=*, on all nodes even if those nodes are merely parts of ways. This import tagging scheme became less popular after the bloated TIGER node tags, introduction of changeset tags, and recommendations for dedicated import user accounts (see import guidelines).