November 2005

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This dataset is a digital hydrologic unit boundary layer that is at the Subwatershed (12-digit) level. The layer also includes delineations at the Watershed (10-digit) and Subbasin (8-digit) levels. Each basin is identified by a unique Hydrologic Unit Code (HUC), as well a name, at each level. HUCs are identifiers as assigned to basin polygons by the U.S. Geological Survey (USGS).

Data in this layer cover all of Massachusetts and small parts of surrounding states. The names of the statewide datalayers are NRCSHUC_POLY (polygons), NRCSHUC_ARC (arcs), and NRCSHUC_ANNO (annotation).

The HUC is a hierarchical, numeric code that uniquely identifies hydrologic units. Hydrologic units are subdivisions of watersheds nested from largest to smallest areas and are used to organize hydrologic data.

HUCs are constructed as follows:

 - The first two digits identify the region,
 - the first four digits identify subregions,
 - the first six digits identify accounting units,
 - the first eight digits identify cataloging units,
 - the first ten digits identify watershed units,
 - and the full twelve digits identify subwatershed units.
The USGS has developed the first 8-digit HUC for the United States, while the U.S. Department of Agriculture, Natural Resource Conservation Service (USDA-NRCS) within each state is developing the full 12-digit HUC. For more details please see Information about Hydrologic Units and the Watershed Boundary Dataset from the USDA.


The original data set was developed by the USDA-NRCS, by delineating the boundary lines on base USGS 1:24,000 scale topographic quadrangle maps, and digitizing the delineated lines. Digital Raster Graphics (DRG) images were used for edits to the data layer. The dataset produced by the joint NRCS-USGS effort to develop the 12-digit national standard is known as the Watershed Boundary Datalayer (WBD).

For ease of use and purposes of symbology and labeling, MassGIS dissolved the full polygon layer into three additional layers. Each contains features delineated at one of the three HUC levels: NRCSHUC10_POLY, NRCSHUC12_POLY and NRCSHUC8_POLY.


The polygon attribute table for NRCSHUC_POLY has the following fields:
Field Name Description
HUC_8 8-digit HUC
HU_8_STATE HUC 8 State:
 CT = Connecticut
 MA = Massachusetts
 NH = New Hampshire
 NY = New York
 RI = Rhode Island
 VT = Vermont
HU_8_DS Downstream HUC Subbasin Level 4 (8-digit)
HU_8_NAME HUC 8 Basin Name
HU_8_MOD Hydrologic Unit Modifications Subbasin Level 4 (8-digit) (Not coded)
HU_8_TYPE Hydrologic Unit Type Subbasin Level 4 (8-digit) (Not coded)
HUC_10 10-digit HUC
HU_10_STAT HUC 10 State (same values as HU_8_STATE)
HU_10_DS Downstream Hydrologic Unit Code Watershed Level 5 (10-digit)
HU_10_NAME HUC 10 Basin Name
HU_10_MOD Hydrologic Unit Modifications WATERSHED Level 5 (10-digit):
 BC = Barge Canal
 DM = Dam at outlet or HU boundary
 IT = Interbasin Transfer
 NM = No Modifications
 PD = Pipe Diversion
HU_10_TYPE Hydrologic Unit Type Watershed Level 5 (10-digit):
 F = Frontal hydrologic unit
 S = Standard hydrologic unit
HUC_12 12-digit HUC
ACRES Area of polygon in acres
HU_12_STAT HUC 12 State (same values as HU_8_STATE)
HU_12_DS Downstream Hydrologic Unit Code Subwatershed Level 6 (12-digit)
HU_12_NAME HUC 12 Basin Name
HU_12_MOD Hydrologic Unit Modifications Subwatershed Level 6 (12-digit)
 (same values as HU_10_MOD)
Hydrologic Unit Type Subwatershed Level 6 (12-digit):
 F = Frontal hydrologic unit
 S = Standard hydrologic unit
 W = Water hydrologic unit
FIPS_C County codes

Each of the three polygon layers delineated at the individual HUC levels contain only the fields relevant for its level.

In the arc attribute table, the field OUTLINE is coded as follows:

Field Name Description
 Boundary type:
8 8-digit HUC boundary
10 10-digit HUC boundary
12 12-digit HUC boundary
4 Coastline


MassGIS maintains the layer, although no updates are planned.

For other watershed data, see these layers:

Last Updated 1/10/2017