From OpenStreetMap Wiki
Jump to navigation Jump to search
Public-images-osm logo.svg ref:US:NID
United States Army Corps of Engineers logo.svg
US National Inventory of Dams ID number Show/edit corresponding data item.
Group: references
URL pattern$1/summary
Used on these elements
may be used on nodesmay be used on waysmay be used on areas (and multipolygon relations)may be used on relations
Status: in use

The National Inventory of Dams is maintained by the U.S. Army Corp of Engineers and has an ID number for each dam they've cataloged in the United States.


From the National Inventory of Dams Data Dictionary:

The official NID identification number for the dam, known formerly as the National ID. This is a required field, and must have an entry for each dam included in the NID. The State Dam Safety Offices assign and maintain the NID IDs for all dams, regardless of ownership. The first two characters of the identity are the two-letter state abbreviation, based on the location of the dam. The last five to six characters of the identity are a unique number (AB#####); although States are allowed to use alphanumeric combinations in the characters that follow the state abbreviation.

Additionally, some dams are represented as separate parts in different locations but with a common NID ID. These will also have an 'Other Structure ID' which can be combined with the main NID ID to form a 'Federal ID' which the formatter URL for this tag will also accept.

Other Structure ID

The identification number (S001, S002, etc.) of a separate structure, such as a saddle dam or dike, associated with the dam project. This field applies only to saddle dams, dikes or other separate structures associated with a primary dam. This field is blank for all other dams.

Federal ID

The unique identifier for each dam record. For saddle dams, dikes or other separate structures associated with the dam project, it is a concatenation of the primary dam’s NID ID and the Other Structure ID. For all other dams, it is the NID ID.


This tag can be added to waterway=dam or waterway=weir objects.

Example value

ref:US:NID=NV10122 for the Hoover Dam, way 49938932

Information about the dam can be looked up using the url<ID NUMBER>/summary. For example: NV10122 at the National Inventory of Dams

Useful data

Some of the information stored in the NID can be helpful when trying to draw a dam in OSM.

  • Dam Type: On the "Summary" page. "Earth" is by far the most common. Other common types are "gravity," "concrete," and "rockfill." An "earth" type dam can confirm what is visible on satellite: that the dam is the mound of earth on or right next to the edge of their body of water.
  • Other Names and Former Names: On the "Description" tab, these two fields can be useful when the dam is named something different than the nearest body of water or if the dam in OSM is currently only a node imported from GNIS years ago.
  • Latitude and Longitude: On the "Description" tab under "Geography".
  • River or Stream Name: Also on the "Description" tab in the "Geography" section. This can be useful if satellite imagery doesn't make it immediately obvious where the dam is but you can see the named waterway passing through the area. The NID appears to be a well-maintained resource, however sometimes the latitude and longitude they provide isn't as close to the dam in question as it could be.
  • Dam Length (Ft): On the "Structure" tab, the length of the dam in feet can help confirm that the dam is where it appears to be on satellite; i.e. a long mound of dirt next to a lake, or even just the edge of the lake itself nearest the latitude and longitude provided. Many times if a lake has one flat side, this number will be very close to its length. While useful in these ways, this measurement is not always perfect. A dam in OpenStreetMap that does not match its length stated in the NID doesn't have anything wrong with it by that fact alone.

More example dams:

Dams with more than one structure

Some dams that are already drawn separately will share an NID ID. These can be tagged with the federal ID (NID ID + Other Structure ID). For example:

See also

US National Inventory of Dams

External links