# properties.id.description
Hydrologic unit code. The format of the code is ('RRSSBBUUWWXX') where: 'RR' is the 2-digit code for the region. 'SS' is the 2-digit code for the sub-region. 'BB' is the 2-digit code for the basin. 'UU' is the 2-digit code for the sub-basin. 'WW' is the 2-digit code for the watershed. 'XX' is the 2-digit code for the sub-watershed. Watersheds are delineated by USGS using a nationwide system based on surface hydrologic features. This system divides the country into 22 regions (2-digit), 245 subregions (4-digit), 405 basins (6-digit), ~2,400 subbasins (8-digit), ~19,000 watersheds (10-digit), and ~105,000 subwatersheds (12-digit). A hierarchical hydrologic unit code (HUC) consisting of 2 additional digits for each level in the hydrologic unit system is used to identify any hydrologic area (see Federal Standards and Procedures for the National Watershed Boundary Dataset - https://pubs.usgs.gov/tm/11/a3/).