Difference between res_only and aianhh?

What is the difference between the two geographic levels within “NATIVE AMERICAN/ALASKAN/HAWAIIAN”? And is there accompanying documentation that explains these differences? I couldn’t seem to find anything from IPUMS or the Census - just explanations for what the various different subcategories of Native land meant within these files respectively.

The two different geographic levels are:

“AMERICAN INDIAN AREA/ALASKA NATIVE AREA (RESERVATION OR STATISTICAL ENTITY ONLY” (res_only)

“AMERICAN INDIAN AREA (OFF-RESERVATION TRUST LAND ONLY)/HAWAIIAN HOME LAND” (aianhh)

It is unclear how the “res_only” file is different than the “aianhh” file and why those differences exist.

There are three relevant geographic levels involved in your question:

“AMERICAN INDIAN AREA/ALASKA NATIVE AREA/HAWAIIAN HOME LAND” (aianhh)

“AMERICAN INDIAN AREA/ALASKA NATIVE AREA (RESERVATION OR STATISTICAL ENTITY ONLY” (res_only)

“AMERICAN INDIAN AREA (OFF-RESERVATION TRUST LAND ONLY)/HAWAIIAN HOME LAND” (trust)

Note that “aianhh” is the ID for the first of these and “trust” is the ID for the last one.

There’s some information about these levels in the source documentation on the NHGIS Tabular Data Sources page for any of the summary files that provide data at these levels. Most recently, in the 2020 Census National Redistricting Data Summary File Technical Documentation, these areas are explained on pages 81-85.

In short:

  • The ‘aianhh’ level encompasses all American Indian, Alaska Native, and Native Hawaiian areas.
  • Every ‘aianhh’ area is classified as either a ‘reservation or statistical entity’ or an ‘off-reservation trust land/Hawaiian home land’
  • The ‘res_only’ level covers only the first of these area types, and the ‘trust’ level covers the second
  • The combination of ‘res_only’ and ‘trust’ lands matches the complete ‘aianhh’ level

The TIGER/Line files that are the source of NHGIS boundary files provide a shapefile only for the complete ‘aianhh’ level. (TIGER/Line uses a slightly different shorthand of “AIANNH”). NHGIS constructs its ‘res_only’ and ‘trust’ boundary files by splitting the AIANNH source file in two.