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;