Data Dictionary Model v 2.1

This document is a companion to the NHD v 2.1 Schema. It provides descriptions for all the feature classes and attribute tables found in the NHD, including the WBD feature dataset which replaces the Hydrologic Units feature dateset in version 2.1. This format is easy to use for day to day activities. However, the NHD Data Model Schema includes the full value domains and all the links and relationships between the feature classes and tables that are necessary to fully understand the NHD. Related documents include:

Field Name	Definition	Applies to	Comments
Permanent_ Identifier	40-char GUID value that uniquely identifies the occurrence of each feature in The National Map. National Database primary key.	All feature classes	Locally assigned during new data creation (features already assigned a ComID retain that value as the Permanent_ Identifier)
FDate	Date of last feature modification.	All feature classes
Resolution	Source resolution. Currently NHD is available as separate resolutions. Plans are to develop a single-resolution database with the highest resolution data that can be generalized.	All feature classes	Domain of values: 1= Local >1:12,000 2= High 1:24,000/12,000 3= Medium 1:100,000
GNIS_ID	Unique identifier assigned by GNIS, 10-char value.	All feature classes	GNIS_ID = “null” if no name associated with the feature
GNIS_Name	Proper name, specific term, or expression by which a particular geographic entity is known, length 65.	All feature classes	GNIS_Name = “null” if no name is associated with the feature
LengthKM	Length of linear feature based on Albers Equal Area, length 8.	NHDFlowline NHDLine	Computed
AreaSqKm	Area of areal feature based on Albers Equal Area, length 8.	NHDArea NHDWaterbody	Computed
Elevation	The vertical distance from a given datum.	NHDArea NHDWaterbody	Stage of the water elevation is encoded in the FCode.
ReachCode	Unique identifier. The first eight digits are the WBD_HUC8. The next six digits are randomly assigned, sequential numbers that are unique within a HUC8, length 14.	NHDFlowline NHDWaterbody NHDPoint	Required for NHDFlowlines. NHDWaterbody and NHDPoint feature classes allow reach codes, but they are not required.
FlowDir	Direction of flow relative to coordinate order, length 4.	NHDFlowline	Domain of values: 1 = With digitized 0 = Uninitialized
WBArea_ Permanent_ Identifier	Permanent_Identifier of the waterbody Through which the flowline flows		Only applies to Artificial Path feature type
FType	Three-digit integer value; unique identifier of a feature type.	All feature classes	Click here for the feature catalog
FCode	Five-digit integer value; comprised of the feature type and combinations of characteristics and values.	All feature classes	Click here for the feature catalog

Field Name	Definition	Applies to	Comments
Permanent_ Identifier	40-char GUID value that uniquely identifies the occurrence of each feature in The National Map.	All feature classes	Locally assigned during data creation (features already assigned a ComID retain that value as the Permanent_ Identifier)
EventDate	Date an event was created.	All feature classes
ReachCode	Reach Code on which the event is located.	All feature classes
ReachSMDate	Reach Version Date	All feature classes	The version date tracks the last time that the reach represented by ReachCode experienced a change in geometry. When the ReachSMDate in the event record and the ReachSMDate in the NHDReachCode_ComID table disagree, the position of the event along the network may need to be updated.
ReachResolution	Source resolution.	All feature classes	Domain of values: 1 = Local >1:12,000 2 = High 1:24,000/12,000 3 = Medium 1:100,000
Feature_Permanent_IIdentifier	Permanent_Identifier of NHD feature that is referenced as an event.		Features from NHDPoint and NHDLine may be referenced to the network through an event feature.
FeatureClassRef	NHD feature class that holds FeatureComID	All feature classes
SourceOriginator	Originator of the event	All feature classes
SourceDataDesc	Description of the entity	All feature classes
Source_FeatureID	Identifier of the entity used in the source data.	All feature classes
FeatureDetailURL	URL where detailed event entity data can be found	All feature classes
Measure	Measure along the reach, in percent from downstream end, where a point event is located.	Point Event feature class
FMeasure	Measure along the reach, in percent from downstream end, where a linear event begins (from).	Line Event feature class
TMeasure	Measure along the reach, in percent from downstream end, where a linear event ends (to).	Line Event feature class
EventType	Type of entity in an event	All feature classes
EventOffset	Distance from the network to be used to display event	Point and Line Event feature classes	Negative offsets display the event to the left of the network and positive offsets display the event to the right of the line. Offsets are useful for displaying overlapping events.

Field Name	Definition	Applies to	Comments
Gaz_ID	Unique identifier assigned by GNIS, length 10.	All feature classes
Area_Acres		All feature classes
Area_SqKm		All feature classes
States		All feature classes
LoadDate		All feature classes
HUC_X	Numeric identifier for each level (2,4,6,8,10, and 12) of hydrologic units	All feature classes
HU_X_Name	Name assigned to each level (2,4,6,8,10, and 12) of hydrologic units	All feature classes
HU_X_Type	Geomorphic and other considerations used to develop the hydrologic unit.	HU10, HU12, HU14, HU16
HU_X_Mod	A two-character, uppercase abbreviation(s) for either (1) the type of modification to natural overland flow that alters the location of a Watershed boundary or (2) the special conditions GF-ground-water flow, GL-glacier, IF-ice field, OF-overbank flow, KA-karst, NC-noncontributing area, and IT-interbasin transfer	HU10, HU12, HU14, HU16
NContrib_Acres	Area that does not flow toward the outlet of a hydrologic unit.	HU12, HU14, HU16
NContrib_SqKm	Area that does not flow toward the outlet of a hydrologic unit.	HU12, HU14, HU16
HU_2 are not included with the data HU_14 and HU_16 are included only where created by local stewards.

Field Name	Definition	Applies to	Comments
FCode	Five-digit integer value; comprised of the feature type and combinations of characteristics and values.	All feature types	Only some features have attributes; last two digits are “00” if no additional values are encoded.
Description	Character string that contains all the characteristics and values associated with a feature code.	All feature types	Only some features have attributes; only feature type is used if no additional values are encoded.
In addition to the full description, there is a text field for each characteristic associated with a feature code. The name of each field is the name of the characteristic. By default, the attribute tables for the feature classes display the text string for the FType and Fcode. This was done to make the data more user friendly. Users may toggle between the text string and the code.
CanalDitchType	Function or purpose	Canal/Ditch
ConstructionMaterial	Predominant material used	Dam/Weir and Reservoir
HydrographicCategory	Portion of the year the feature contains water	Stream/River, Lake/Pond, Reservoir and Swamp/Marsh
InundationControlStatus	Existence of functional control structures	Inundation Area
OperationalStatus	State or condition	Special Use Zone
PipelineType	Function or purpose	Pipeline
PositionalAccuracy	The accuracy within which a feature may be confidently positioned	Sounding Datum Line and Underground Conduit
RelationshipToSurface	Vertical location relative to the surface	Pipeline and Rock
ReservoirType	Function or purpose	Reservoir
Stage	Height of water surface	Inundation Area and Lake/Pond
SpecialUseZoneType	Function or purpose	Special Use Zone

Used for features (i.e. streams and canals) which cross but do not exchange flow

Field Name	Definition	Applies to	Comments
Permanent_ Identifier	Permanent_Identifier of the relationship (relationships already assigned a ComID retain that value as the Permanent_ Identifier)	Vertical Relationship
Above_Permanent_ Identifier	Permanent_Identifier of feature above the vertical offset (feature already assigned a ComID retains that value as the Permanent_ Identifier)	Flowline that is part of vertical relationship
Below_Permanent_ Identifier	Permanent_Identifier of feature below the vertical offset (feature already assigned a ComID retains that value as the Permanent_ Identifier)	Flowline that is part of vertical relationship

Flow table values are derived from the topologic connectivity of the geometric network

Field Name	Definition	Applies to	Comments
DeltaLevel	Numerical difference between stream level for From feature and stream level for To feature		Only populated if stream level has been calculated
Direction	Text or Code to describe direction of flow		In – 709 Network start – 712 Network end - 713 Non-flowing -714
From_Permanent_ Identifier	Permanent_Identifier of feature from which the water flows (feature already assigned a ComID retains that value as the Permanent_ Identifier)
To_Permanent_ Identifier	Permanent_Identifier of feature to which the fetaure flows (feature already assigned a ComID retains that value as the Permanent_ Identifier)

Field Name	Definition	Applies to	Comments
Permanent_Identifier	40-char GUID value that uniquely identifies the occurrence of each feature in The National Map.
ReachCode	Unique identifier. The first eight digits are the WBD_HUC8. The next six digits are randomly assigned, sequential numbers that are unique within a HUC8, length 14.
ReachSMDate	Reach Version Date		The version date tracks the last time that the reach represented by ReachCode experienced a change in geometry.
Resolution	Source resolution. Currently NHD is available as separate resolutions. Plans are to develop a single-resolution database with the highest resolution data that can be generalized
GNIS_ID	Unique identifier assigned by GNIS, length 10.
GNIS_Name	Proper name, specific term, or expression by which a particular geographic entity is known, length 65.

Field Name	Definition	Applies to	Comments
OldReachCode	Reach code prior to change
OldReachDate	Date old reach code was assigned
NewReachCode	Reach code after the change
NewReachDate	Date new reach code was assigned
OldUPMI	Not used
NewUPMI	Not used
ChangeCode	Type of change to the reached feature (A) Add new reach (D) Delete old reach (11) Old reach to new reach (generally used when an existing reach codes was assigned a new reach code in a new subbasin – reach migration) (P1) Part of old reach to new reach (split) (1P) Old reach to part of new reach (merge)
Process	Name of the process that created the reach code change		Many processes to create the NHD were done on the National Database and these have standard codes.
ReachFileVersion	Reach File Version in which the change became effective
OldHUCode	HUC8 of the flowline prior to migration		Used if the flowline was originally assigned a reach code based on an incorrect subbasin assignment
NewHUCode	HUC8 of the flowline prior to migration		Used if the flowline was originally assigned a reach code based on an incorrect subbasin assignment

Contains associations of Permanent_Identifiers to external source Identifiers.

Field Name	Definition	Applies to	Comments
Permanent_ Identifier	40-char GUID value that uniquely identifies the occurrence of each feature in The National Map.
ExternalID	ID that identifies the feature in the source dataset
ExternalIDName	Field name in the external source dataset that contains the unique IDs.
ExternalIDOriginator	Name of the organization or individual who developed the external dataset/features
ExternalEntryDate	Load date of the ExternalID record.
OrganizationType	Code of the organization or individual who developed the external dataset/features		0 = unknown 1 = International 2 = Federal 3 = Tribal 4 = State 5 = Regional 6 = County 7 = Municipal 8 = Private

NHDStatus is used to track data changes for transaction uploads to the central repository. This table is only populated during editing. It is blank when NHD is downloaded for use.

that was used to generate extracted NHD data. This table is most useful to USGS

Field Name	Definition	Applies to	Comments
Meta_ProcessID	40-char GUID value that uniquely identifies a metadata process description in The National Map.
ProcessDescription	Explanation of the event and related parameters or tolerances
ProcessDate	Date when the event was completed.
AttributeAccuracyreport	Explanation of entities and assignments of values in dataset
LogicalConsistencyReport	Explanation of fidelity of relationships in dataset and tests used.
CompletenessReport .	Information about omissions, criteria, definitions used to derive dataset.
HorizPositionalAccuracyReport	Horizontal coordinate measurements and description of tests used.
VertPositionalAccuracyReport	Vertical coordinate measurements and description of tests used.
MetadataStandardName	Name of the metadata standard used to document the dataset.
MetadataStandardVersion	Identification of the version of the metadata standard used to document the dataset.
MetadataDate	Date the metadata was last created or updated.
DataSetCredit	Recognition of those who contributed to the dataset.
ContactOrganization	Name or organization to which type of contact applies.
AddressType	Information provided by the address.
Address	Address line for the address.
City	City of the address
StateOrProvince	State or province of the address
PostalCode	ZIP or other postal code of the address
ContactVoiceTelephone	Telephone number to reach Organization or individual.
ContactInstructions	Supplemental instructions to contact Organization or individual
ContactEmailAddress	E-mail address to reach contact organization or individual.

This table links to process description information found in the NHDMetadata table.

Field Name	Definition	Applies to	Comments
Source_DatasetID	Unique permanent ID value which uniquely identifies a source dataset used in The National Map
Title	Name by which the dataset is known.
SourceCitationAbbreviation	Short form alias for source citation.
Originator	Name of an organization or individual that developed the dataset.
PublicationDate	Date the dataset is published or made available for release.
BeginningDate	First year of the event (if Range_of_Dates applies).		<Null> if CalendarDate is used
EndingDate	Last year for the event (if Range_of_Dates applies).		<Null> if CalendarDate is used
SourceContribution	Brief statement identifying information contributed by source to dataset
SourceScaleDenominator	Denomination of representative fraction on a map.
TypeofSourceMedia	The medium of the source dataset.
CalendarDate	The year (if Single Date applies).		<Null> if BeginningDate and EndingDate are used
SourceCurrentnessReference	Source time period of content information of source dataset is determined.
Meta_ProcessID	Unique permanent ID value which uniquely identifies a process used in The National Map.		Link to the NHDMetadata table

For details on how to use the relationship classes, see Metadata Creation and Use.

The NHD contains the necessary relationships between these tables. For example;

Field Name	Definition	Applies to	Comments
ParameterName			Parameters include Version, Resolution, Processing_Organization, and SchemaVersion
ParameterValue