National Hydrography Dataset

Data Dictionary

 

Data Model version 2.1

 

 

NHD Data Dictionary Quick Start

Data 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:

 

 

This Data Dictionary contains tables for the following items. 

 

Feature DataSets

Hydrography Feature Classes

Hydrography Event Feature Classes

WBD Feature Classes

 

Attribute Tables

NHDFCode

NHDVerticalRelationship

NHDFlow

NHDFlowlineVAA

NHDReachCodeMaintenance

NHDReachCrossReference

NHDStatus

NHDProcessingParameters

NHDMetadata

NHDFeatureToMetadata

NHDSourceCitation

ExternalCrosswalk

 

Relationship Classes

NHDFeature to Metadata

NHDMetadata Has Source Citation


 

Hydrography Feature Classes

NHDPoint, NHDLine, NHDFlowline, NHDWaterbody, NHDArea

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

 

Hydrography Event Feature Classes

NHDPointEvent, NHDLineEvent, NHDAreaEvent

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.

 

 

 


 

WBD

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.

 


Attribute Tables

 

NHDFCode

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

 

 


 NHDVerticalRelationship

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

 

 

NHDFlow

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

 and values of FlowDir attribute of NHDFlowline features

This table is not populated in pre-processed subregions

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)

 

 

 

 

NHDReachCodeMaintenance

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.

 

 

 


NHDReachCrossReference

 Information that tracks changes, over time, to reach codes.

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

 

 

 

 

ExternalCrosswalk

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

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.

Field Name

Definition

Applies to

Comments

ID

Temporary ID assigned to track feature edits.

Edited features

When edits are loaded into the national database, the temporary ID is replaced with an official ComID

Permanent_Identifier

40-char GUID value that uniquely identifies the occurrence of each feature in The National Map.

 

 

Status

Type of edit

Edited features

 

 

 

 

 

 

 

NHDProcessingParameters

This table lists the schema and the version of the master NHD database

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

to verify the version used by data stewards for updates.

Field Name

Definition

Applies to

Comments

ParameterName

 

 

Parameters include Version, Resolution, Processing_Organization, and SchemaVersion

ParameterValue

 

 

 

 

NHDMetadata

This table contains FGDC compliant Data Quality information

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.

 

 

 

NHDFeatureToMetadata

This table links every feature in the NHD to one or many metadata records.

Field Name

Definition

Applies to

Comments

Permanent_Identifier

40-char GUID value that uniquely identifies the occurrence of each feature in The National Map.

 

 

Meta_ProcessID

Unique ID for a metadata process descritpion

 

Features are associated to specific process descriptions. The Meta_processID links to the NHDMetadata table.

 

 

 

NHDSourceCitation

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

Not all process descriptions have a source citation.

Content is based on FGDC Metadata requirements

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

 

Relationship Classes

To help users discover the feature-based metadata records,

explicit relationship classes are created.

 

Feature-level metadata requires three tables:

NHDFeatureToMetadata

NHDMetadata

NHDSource Citation

 

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;