Hydrological code: Difference between revisions

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The original delineation of units, down to subbasins (cataloging units), was done using 1:250,000 [[Scale (map)|scale]] maps and data. The newer delineation work on watersheds and subwatersheds was done using 1:24,000 scale maps and data.{{Contradiction inline|This page says below that the newer delineation work on watersheds was done at a "higher resolution" but 1:24,000 is a lower resolution than 1:250,000.|date=October 2015}} As a result, the subbasin boundaries were changed and adjusted in order to conform to the higher resolution watersheds within them. Changes to subbasin boundaries resulted in changes in area sizes. Therefore, older data using "cataloging units" may differ from newer, higher resolution data using "subbasins".<ref name="WBDstandard">{{cite web |url=https://pubs.usgs.gov/tm/11/a3/pdf/tm11-a3.pdf|title= Federal guidelines, requirements, and procedures for the national Watershed Boundary Dataset: U.S. Geological Survey Techniques and Methods 11–A3 |last=|first=|date=|year=2009|website=|publisher= [[Natural Resources Conservation Service]] and [[United States Geological Survey]] |yeararchive-url= 2009 |urlarchive-date= https://pubs.usgs.gov/tm/11/a3/pdf/TM11|dead-A3.pdf url=|accessdate= 4 November 2010}}</ref>

[[Image:Huc region-edit.png|thumb|right|The 21 top-level 2-digit "region" hydrologic unit boundaries. The names are as follows: 01 New England, 02 Mid-Atlantic, 03 South Atlantic-Gulf, 04 Great Lakes, 05 Ohio, 06 Tennessee, 07 Upper Mississippi, 08 Lower Mississippi, 09 Souris-Red-Rainy, 10 Missouri, 11 Arkansas-White-Red, 12 Texas-Gulf, 13 Rio Grande, 14 Upper Colorado, 15 Lower Colorado, 16 Great Basin, 17 Pacific Northwest, 18 California, 19 Alaska, 20 Hawaii, 21 Caribbean.]]