NHDFlowlines consist of routes that make up a linear surface water drainage network. Flowlines have a reach code and a measure, allowing for the establishment of upstream/downstream relationships. This network allows for powerful analysis and modeling capabilities. Each Feature type is attributed with descriptive information by an Fcode.


See a complete list of Fcodes for hydrography features.

The arrows on these Flowlines point in the possible direction of flow when flow

 direction is initialized. Flow direction arrows may be symbolized in the feature

 properties or by using the Utility Network Analyst.


 The attributes associated with NHDLines are as follows:

Field Name



Permanent Identifier

Global ID and GUID data types store registry style strings consisting of 36 characters enclosed in curly brackets. These strings uniquely identify a feature or table row within a geodatabase and across geodatabases. This is how features are tracked in one-way and two-way geodatabase replication.



Date of last feature modification.



Source resolution.  Currently NHD is available as separate resolutions.  Plans are to develop a single-resolution database holding the highest resolution data with tools to allow for generalization

Domain of values:

Local >1:12,000

High 1:24,000/12,000

Medium 1:100,000


Unique identifier assigned by GNIS, length 10.

GNIS_ID = “null” if no name associated with the feature


Proper name, specific term, or expression by which a particular geographic entity is known, length 65.

GNIS_Name = “null” if no name associated with the feature


Length of linear feature based on Albers Equal Area, length 8.



Unique identifier composed of two parts.  The first eight digits is the subbasin code as defined by FIPS 103.  The next six digits are randomly assigned, sequential numbers that are unique within a subbasin, length 14. 

Required for all NHDFlowlines.

NHDWaterbody and NHDPoint feature classes allow reach codes, but does not require them.


Direction of flow relative to coordinate order, length 4.

Domain of values:

With digitized



Three-digit integer value; unique identifier of a feature type.



Five-digit integer value; composed of the feature type and combinations of characteristics and values.



 Length in meters

All features should have a + integer value


Created when Geometric Network is built

All features should be set to True (From the database).

New or modified features will have a Null value until network is rebuilt.