FGDC-STD-014.6-2008

Geographic Information Framework Data Content 

Standard 

Part 6: Hydrography 

May 2008 
ii

Federal Geographic Data Committee 

Established by Office of Management and Budget Circular A-16, the Federal Geographic Data 

Committee (FGDC) promotes the coordinated development, use, sharing, and dissemination of 

geographic data. 

The FGDC is composed of representatives from the Departments of Agriculture, Commerce, 

Defense, Education, Energy, Health and Human Services, Homeland Security, Housing and 

Urban Development, the Interior, Justice, Labor, State, and Transportation, the Treasury, and 

Veteran Affairs; the Environmental Protection Agency; the Federal Communications Commission; 

the General Services Administration; the Library of Congress; the National Aeronautics and 

Space Administration; the National Archives and Records Administration; the National Science 

Foundation; the Nuclear Regulatory Commission; the Office of Personnel Management; the Small 

Business Administration; the Smithsonian Institution; the Social Security Administration; the 

Tennessee Valley Authority; and the U.S. Agency for International Development. Additional 

Federal agencies participate on FGDC subcommittees and working groups. The Department of 

the Interior chairs the committee. 

FGDC subcommittees work on issues related to data categories coordinated under the circular. 

Subcommittees establish and implement standards for data content, quality, and transfer; 

encourage the exchange of information and the transfer of data; and organize the collection of 

geographic data to reduce duplication of effort. Working groups are established for issues that 

transcend data categories. 

For more information about the committee, or to be added to the committee's newsletter mailing 

list, please contact: 

Federal Geographic Data Committee Secretariat 

c/o U.S. Geological Survey 

590 National Center 

Reston, Virginia 22092 

Facsimile: (703) 648-5755 

Internet (electronic mail): fgdc@usgs.gov 

 World Wide Web: http://www.fgdc.gov
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Geographic Information Framework Data Content Standard 

Part 6: Hydrography

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Contents 

Introduction................................................................................................................................... vi

1 Scope, purpose, and application .............................................................................................. 1

1.1 Scope................................................................................................................................. 1

1.2 Purpose ............................................................................................................................. 1

1.3 Capabilities supported by this part of the standard ..................................................... 1

1.3.1 Minimize duplications of data and application development ...................................... 2

1.3.2 Simplify interchange of hydrography data and related information........................... 2

1.3.3 Overcome difficulties in integrating data....................................................................... 2

1.3.4 Improve support for analytic activities .......................................................................... 2

1.3.5 Manage multiple representations of features................................................................ 3

2 Normative references................................................................................................................. 3

3 Maintenance authority ............................................................................................................... 3

3.1 Level of responsibility...................................................................................................... 3

3.2 Contact information ......................................................................................................... 3

4 Terms and definitions ................................................................................................................ 3

5 Symbols, abbreviated terms, and notations............................................................................ 5

6 Requirements.............................................................................................................................. 6

6.1 UML class diagram: a data model for hydrography ..................................................... 6

6.2 UML objects ...................................................................................................................... 7

6.2.1 HydroCollection................................................................................................................ 7

6.2.2 HydroFeature .................................................................................................................... 8

6.2.3 HydroElement ................................................................................................................... 9

6.2.4 HydroComplex ................................................................................................................ 10

6.2.5 FeatureRelationship....................................................................................................... 11

6.2.6 Event................................................................................................................................ 11

6.2.7 MeasuredEvent ............................................................................................................... 13

6.2.8 UnmeasuredEvent .......................................................................................................... 14

6.2.9 Name................................................................................................................................ 15

6.2.10 Representation ........................................................................................................... 15

6.2.11 Measurement .............................................................................................................. 16

6.2.12 ComputedNetworkValues.......................................................................................... 17

6.2.13 Common framework classes .................................................................................... 20

6.2.14 External packages...................................................................................................... 20

6.2.15 Code lists and enumerations.................................................................................... 20

6.3 Example hydrography data ........................................................................................... 22

Annex A (normative) Feature codes, code lists, and enumerations...................................... 23

A.2.1 General ............................................................................................................................ 26

A.2.2 Feature code lists ........................................................................................................... 26

A.2.2.1 CompositeType code list........................................................................................... 26

A.2.2.2 EventType code list ................................................................................................... 26

A.2.2.3 HydroFeatureType code list...................................................................................... 28

A.2.2.4 RelationshipType code list........................................................................................ 32

A.2.2.5 UnitsType code list .................................................................................................... 32

A.2.3 FlowCode enumeration.................................................................................................. 32

Annex B (informative) Design concepts and design requirements ....................................... 33

Annex C (informative) Bibliography .......................................................................................... 37
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Figures 

Figure 1 – Main UML classes for hydrography........................................................................... 6

Figure 2 – Hydrography UML class code lists and enumerations ......................................... 21

Figure 3 – Example basic hydrographic data........................................................................... 22

Tables 

Table 1 – Data dictionary for HydroCollection ........................................................................... 7

Table 2 – Data dictionary for HydroFeature................................................................................ 8

Table 3 – Data dictionary for HydroElement............................................................................... 9

Table 4 – Data dictionary for HydroComplex............................................................................ 10

Table 5 – Data dictionary for FeatureRelationship................................................................... 11

Table 6 – Data dictionary for Event ........................................................................................... 11

Table 7 – Data dictionary for MeasuredEvent........................................................................... 13

Table 8 – Data dictionary for UnmeasuredEvent...................................................................... 14

Table 9 – Data dictionary for Name ........................................................................................... 15

Table 10 – Data dictionary for Representation......................................................................... 15

Table 11 – Data dictionary for Measurement............................................................................ 16

Table 12 – Data dictionary for ComputedNetworkValues ....................................................... 17 

Table A.1 – Common feature codes........................................................................................... 23

Table A.2 – CodeList for CompositeType ................................................................................. 26

Table A.3 – CodeList for EventType .......................................................................................... 27

Table A.4 – CodeList for HydroFeatureType ............................................................................ 28

Table A.5 – CodeList for RelationshipType .............................................................................. 32

Table A.6 – CodeList for UnitsType........................................................................................... 32

Table A.7 – FlowCode enumeration........................................................................................... 32 

Table B.1 – Design requirements............................................................................................... 33
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Geographic Information Framework Data Content Standard 

Part 6: Hydrography

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Foreword 

Geographic information, also known as geospatial information, both underlies and is the subject 

of much of the political, economic, environmental, and security activities of the United States. In 

recognition of this, the United States Office of Management and Budget issued Circular A-16 

(revised 2002), which established the Federal Geographic Data Committee (FGDC) as a 

coordinating organization. 

Work on this standard started under the Geospatial One-Stop e-Government initiative. The 

standard was developed with the support of the member agencies and organizations of the 

FGDC and aids in fulfilling a primary objective of the National Spatial Data Infrastructure (NSDI), 

that is, creation of common geographic base data for seven critical data themes. The seven core 

data themes are considered framework data of critical importance to the spatial data 

infrastructure. 

As the Geographic Information Framework Data Content Standard was developed using public 

funds, the U.S. Government will be free to publish and distribute its contents to the public, as 

provided through the Freedom of Information Act (FOIA), Part 5 United States Code, Section 552, 

as amended by Public Law No. 104-231, “Electronic Freedom of Information Act Amendments of 

1996”. 
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Introduction 

The primary purpose of this part of the Geographic Information Framework Data Content 

Standard is to support the exchange of surface water (hydrography) data. This part seeks to 

establish a common baseline for the semantic content of hydrography databases for public 

agencies and private enterprises. It also seeks to decrease the costs and simplify the exchange 

of hydrography data among local, Tribal, State, and Federal users and producers. That, in turn, 

discourages duplicative data collection. Benefits of adopting this part of the standard also include 

the long-term improvement of the geospatial hydrography data through the establishment of Web 

data services for hydrography data and maps within the community. 

The Hydrography part describes the geographic locations, interconnectedness, and 

characteristics of features in the surface water system. The hydrography system includes 

physical and logical components representing the flow and presence of water within the surface 

water portion of the environment. This part, and the included UML model, is a result of 

contributions from a variety of information and systems models. These include: the National 

Hydrography Dataset (NHD), the Pacific Northwest Framework (PNW), the ArcHydro data model, 

and the Geographic Names Information System (GNIS). The development of a shared database 

would be accomplished through “alliances” of data providers. 
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Part 6: Hydrography

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1 Scope, purpose, and application 

1.1 Scope 

The purpose of Geographic Information Framework Data Content Standard, Part 6: Hydrography 

is to establish the content requirements for the collection and interchange of hydrography 

features and to facilitate the maintenance and use of that information by all users of geographic 

information. The Hydrography part identifies and defines terminology, encoding schema, and the 

data components required for describing hydrographic features, along with the metadata needed 

for the hydrography data exchange. This part specifies the content and its organization 

necessary for the successful interchange of hydrography data. This part does not specify a 

particular structure for the storage of hydrography data. The scope of this part is limited to the 

information regarding surface water features and hydrographic networks for the purpose of 

cartography and network analysis. This part is intended to be applicable at a variety of scales. 

1.2 Purpose 

The goal of the Hydrography part of the Framework Data Content Standard is to provide common 

definitions and syntax to enable collaborative development, use, and exchange of hydrography 

data. This part defines the components of networked and non-networked surface water features, 

one of seven NSDI framework themes. The primary purpose of the part is to support the 

exchange of hydrographic feature and network information by general and expert users. It is the 

intent of the part to set a common baseline of information content for exchange within the 

hydrographic community that will enhance data sharing and applications development when used 

with standards-based Web services or file transfer. 

The determination of “best-available” hydrography data depends on the usage or organizational 

requirements and is thus not addressed by the Hydrography part. It is anticipated that multiple 

representations of hydrographic features will exist within the broader community. Policies have 

been or will be established for describing, maintaining, and exchanging the various 

representations of features within specific application communities, such as the NHD. This part 

will accommodate the exchange of these multiple representations. 

While collection criteria could be linked to each feature to give some guidance as to quality 

characteristics, this part does not specify the criteria by which each feature would be captured 

(see capture conditions in definitions). Building on the intention to define common community 

framework content, this part defines a data content model for the exchange of agreed-upon 

thematic data, rather than the endorsement of a particular native database content design. This 

part supports the mapping and conversion of native data in any format into a common 

representation for exchange over the Web or as files. Encoding of hydrography data for transfer, 

based on the models in this part, is described in the Base Document (Part 0) of the Framework 

Data Content Standard. 

The audience of this part of the standard includes hydrography data users, maintainers, and 

distributors. The content is intended to support the general requirements of natural resource 

managers, environmental and water resources agencies, and hydrography applications designers 

and developers. Specific guidance on the implementation of this part for specific user 

communities will be made through external guidance or policy documents. 

1.3 Capabilities supported by this part of the standard 

The development of this part of the Framework Data Content Standard will greatly assist in 

mitigating the following issues, as determined by the Hydrography Modeling Advisory Team 

(MAT) – a group of domain experts convened to define a common set of hydrography information 

content: 

• Duplication of data and application development 

• Complications exchanging hydrography framework data and related information 
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• Difficulties integrating data 

• Poor framework/support for analytic activities 

• Difficulties managing multiple representations of features 

1.3.1 Minimize duplications of data and application development 

Duplication of data and application development refers to duplicative efforts required, in the 

absence of a content standard, to store and manage data and develop applications for their use. 

Parties sharing data who add, edit, or remove features from base data, for example, can be 

forced to manage duplicate datasets because no dataset conforms to a standard and because 

there is no agreed upon protocol for replacing or archiving datasets as they are amended. 

Similarly, applications can be developed and re-developed to meet the same business needs as 

data models change. 

1.3.2 Simplify interchange of hydrography data and related information 

The original wording of this objective used the term “share” instead of “exchange.” “Share” was 

thought to refer to the institutional arrangements and attendant administrative issues required for 

organizations to provide one another with data. This meaning was deemed outside this part of 

the standard’s scope, although perhaps appropriate for an informative annex. “Co-managing” (for 

example, managed by more than one party) was similarly considered for discussion in this part. 

Because of the significant maintenance arrangements it implies, this topic should be handled as 

the subject of a separate document. “Interchange” was selected because it was thought to 

convey the central meanings of giving, taking, and replacing data between individuals or systems. 

The phrase “related information” was also added to the original wording to cover situations when 

hydrography data users exchange fish data, environmental information, point sampling locations, 

protected status, and so on, along with base hydrography data. 

1.3.3 Overcome difficulties in integrating data 

The MAT identified four possible meanings of “integrating” which should be addressed by this 

part of the Framework Data Content Standard: 

• Overlapping data of similar content 

• Processing adjacent data 

• Handling or arbitrating different scale data 

• Conflation 

It was agreed that to make the data model extensible, this part should tie attribution to an 

identifier. The measure of this objective would be whether or not users can understand and use 

the resultant data. 

1.3.4 Improve support for analytic activities 

The MAT clarified the meaning of this objective as supporting critical uses and meeting the 

business needs of managers for decision making. By contrast to the other objectives, this 

objective is broader than objectives pertaining to data and datasets alone. 

Participants noted that measuring this objective will be difficult because a standard’s capacity to 

support analytic activities depends on and varies with data and business needs. It is also 

important to note that users’ business and decision making needs are too varied and numerous to 

be equally supported by this part of the standard. The goal of the framework standardization 

activity is to identify the intersection of information content for exchange that is universally useful 

within a community. Based on this approach as opposed to a union approach, this part can 

reasonably be expected to support certain common business and decision-making needs, but not 

all possible needs. 
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1.3.5 Manage multiple representations of features 

The MAT discussed requirements of framework data for managing multiple representations and 

data lineage. It was agreed that a framework model should differentiate data states induced by 

changes over time, scale, or information content. The standard should not require that all 

versions be available, but a user should be able to know what version of data they are 

exchanging. 

2 Normative references 

Annex A of the Base Document (Part 0) lists normative references applicable to two or more parts 

of the standard. Informative references applicable only to the Hydrography part are listed in 

Annex C. Annex D of the Base Document lists informative references applicable to two or more 

of the parts. 

3 Maintenance authority 

3.1 Level of responsibility 

The FGDC is the responsible organization for coordinating work on all parts of the Geographic 

Information Framework Data Content Standard. The development and maintenance authority for 

Part 6: Hydrography is held jointly by the U.S. Geological Survey and U.S. Environmental 

Protection Agency. 

3.2 Contact information 

Address questions concerning this part of the standard to: 

Federal Geographic Data Committee Secretariat 

c/o U.S. Geological Survey 

590 National Center 

Reston, Virginia 20192 USA 

Telephone: (703) 648-5514 

Facsimile: (703) 648-5755 

Internet (electronic mail): gdc@fgdc.gov

WWW Home Page: http://fgdc.gov

4 Terms and definitions 

Definitions applicable to the Hydrography part are listed below. More general terms and 

definitions can be found in the Base Document (Part 0). Users are advised to consult that part for 

a complete set of definitions. 

4.1 

capture conditions 

conditions a feature must meet in terms of measurement or other characteristics before it is 

collected and stored in a dataset 

EXAMPLE A headwater stream collected for a 1:100,000-scale dataset is at least 1 mile long, a lake 

collected for a 1:100,000-scale dataset is at least 6 acres. 

4.2 

complex feature 

feature composed of other features [ISO 19109] 
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4.3 

HydroComplex feature 

group of one or more HydroElement features having attributes, relationships and events that are 

independent of the attributes, relationships and events of the participating features 

NOTE A HydroComplex feature inherits its geometry from the feature or features that it is composed of. 

EXAMPLES reach, watercourse. 

4.4 

HydroElement feature 

instance of a particular hydrography feature type that has geometry that may have attributes, 

relationships, and events 

4.5 

feature code 

numeric value that encodes the unique combination of hydrography feature type and a set of 

feature attribute values 

NOTE The official five-digit hydrography feature code has two parts: the first three digits encode the 

feature type; the last two digits encode values for a set of attributes associated with the feature. See Annex 

A for more information. 

4.6 

line string 

sequence of line segments 

4.7 

reach 

set of one or more hydrographic features grouped into a complex/compound feature that is 

assigned a permanent, public identifier usually referred to as a reach code

NOTE The hydrographic features that compose a reach are selected to maximize their scale 

independence. The reach code is used to link data to a reach and thereby provide an association to other 

related data. When reaches are split or merged, a cross-reference of their permanent identifiers is 

maintained. All linear feature representations of stream/rivers, canal/ditches, pipelines, and all artificial path, 

connector, shoreline, reservoir, and lake/pond features may compose reaches. 

4.8 

reach code 

permanent identifier assigned to reaches

4.9 

stream level 

level within a stream classification system based on the position of the stream within a drainage 

network 

NOTE Stream level is identified by a numeric code such that streams that terminate in sea/ocean 

features are assigned to the lowest level (Level 1) and tributaries are incremented based on the level into 

which they terminate. 

EXAMPLES Mississippi River is a Level 1 stream, the Missouri is a Level 2 stream. 
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4.10 

watercourse 

HydroComplex feature, made up of one or more hydrography features usually based on a name 

attribute 

NOTE Named path or path based on connectivity. Watercourses may be a permanent feature within a 

hydrography dataset. 

5 Symbols, abbreviated terms, and notations 

The following symbols, abbreviations, and notations are applicable to the Hydrography part. 

Symbols, abbreviations, and notations applicable to multiple parts are listed in the Base 

Document (Part 0). 

GNIS – Geographic Names Information System 

GUID – Globally Unique Identifiers 

ID/IDs – Identifier/Identifiers 

NHD – National Hydrography Dataset 

PNW – Pacific Northwest Framework 

SRS – Spatial Reference System 

UUID – Universally Unique Identifiers 
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6 Requirements 

6.1 UML class diagram: a data model for hydrography 

Figure 1, below, illustrates the main UML classes and associations for hydrography. These 

classes, their attributes, and roles are described in detail in the data dictionary (see section 6.2). 

Figure 1 – Main UML classes for hydrography 
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6.2 UML objects Each hydrography UML object is described below. Each description includes a narrative for context and understanding, acontents. 6.2.1 HydroCollection HydroCollection is the container for the features packaged in an exchange of hydrographic information. 

Table 1 – Data dictionary for HydroCollection 

Line Name/Role Name Definition Obligation/ Condition Maximum Occurrence Data Type 

1 HydroCollection Group of features in the exchange <<Feature>> 2 metadata 

Set of formal structured properties that pertain to the collection of features being exchanged 

M 1 CharacterString 

3 Role name: member 

Defines the composition relationship of HydroFeatures within a HydroCollection 

M * <<Abstract>> HydroFeature 
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6.2.2 HydroFeature HydroFeature is an abstract class that captures the characteristics of the hydrographic feature. As the core com

HydroFeature has several significant associations to other classes. HydroFeature has HydroElement and HydroComplex s

Table 2 – Data dictionary for HydroFeature 

Line Name/Role Name Definition Obligation/ Condition Maximum Occurrence Data Type 

4 HydroFeature <<Abstract>> 5 featureID Unique identifier of feature M 1 <<DataType>> Framework::Identifier 6 linkedResource Information related to this feature by URL reference O 1 <<DataType>> Framework:: ExternalResource 7 metadata Descriptive information associated with this feature instance O * CharacterString 8 featureDate Date feature was last modified M 1 Date 9 name Name and naming authority of feature O * Name 10 measure 

Associated calculated measurements of length, height, and area 

O * <<DataType>> Measurement 

11 representation Version of the geometric representation O * <<DataType>> Representation 12 attribute Extended unofficial attribute O * 

<<DataType>> Framework::ExtendedAttribute 

13 Role name: targetFeature Pair association with other feature instance O * FeatureRelationship 14 Role name: event Association to maintain properties on partial HydroFeatures O * <<Abstract>> Event 
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6.2.3 HydroElement Basic hydrographic features with explicit geometry. HydroElement inherits all properties (generalizes) from the HydroFeature. These properties are not included in the table below. 

Table 3 – Data dictionary for HydroElement 

Line Name/Role Name Definition Obligation/ Condition Maximum Occurrence Data Type 

15 HydroElement Basic hydrographic feature with explicit geometry <<Feature>> 16 featureType 

Classification of feature type based on a list of community-defined hydrographic features 

M 1 <<CodeList>> HydroFeatureType 

17 featureCode Numeric code defining feature types and properties O 1 HydroFeatureCode 18 geometry Coordinate representation of the feature M 1 <<Union>> ElementGeometry 19 flowDirection Direction of flow, where known, relative to coordinate ordering O 1 <<Enumeration>> FlowCode 20 Role name: networkAttributes Conditional set of computed hydrologic network values 

C/if FlowCode = 

1 (within 

hydrologic 

network) 

1 <<DataType>> ComputedNetworkValue

21 ElementGeometry The geometry of a feature <<Union>> 22 polygon Bounded surface M 1 <<Type>> GM_Surface 23 point 0-dimensional geometric primitive representing a position [ISO 19107] M 1 <<Type>> GM_Point 24 line M 1 <<Type>> GM_Curve 
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6.2.4 HydroComplex HydroComplex is an aggregate of HydroElement. The HydroComplex may impose property requirements onto the assFor example, a HydroComplex of Reach requires measure values based on the extent of the Reach, not of the HydroEle

Reach. As an aggregate representation, a HydroComplex is retired if the HydroElements that make up the HydroCo

reverse situation does not apply. HydroComplex inherits all properties from the parent abstract class, HydroFeature. Tshown in the table below. 

Table 4 – Data dictionary for HydroComplex 

Line Name/Role Name Definition Obligation/ Condition Maximum Occurrence Data Type 

25 HydroComplex 

Feature composed of HydroElements that does not have its own geometry 

<<Feature>> 

26 compositeType Description of HydroComplex type M 1 <<CodeList>> CompositeType 27 Role name: element 

Aggregation relationship to gather hydrography elements into grouped features such as watercourses 

M * HydroElement 
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6.2.5 FeatureRelationship FeatureRelationship describes binary relationships between feature instances. The order of the elements in the relati

represented using a self-association in the UML model. The RelationshipAttribute qualifier will have relevance to a specific 

Table 5 – Data dictionary for FeatureRelationship 

Line Name/Role Name Definition Obligation/ Condition Maximum Occurrence Data Type 

28 FeatureRelationship Association between feature instances Association 29 type Code for valid relationship type M 1 <<CodeList>> RelationshipType 30 attribute Extended unofficial attribute O * 

<<DataType>> Framework:: ExtendedAttribute 

6.2.6 Event An Event object supports the linking of external attribute information to a portion of a HydroFeature, either HydroElemEvents can be of two types: MeasuredEvent or UnmeasuredEvent. MeasuredEvents are those that reference portions of in the linear reference model. UnmeasuredEvents are those that reference portions of features that do not participate 

model. 

Table 6 – Data dictionary for Event 

Line Name/Role Name Definition Obligation/ Condition Maximum Occurrence Data Type 

31 Event Property whose location falls on or across one or more features <<Abstract>> 32 date Date that provides a reference or version for an event O 1 Date 33 eventID Unique identifier for event M 1 <<DataType>> Framework::Identifier 
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Line Name/Role Name Definition Obligation/ Condition Maximum Occurrence Data Type 

34 relatedURL URL and context for additional information about this property O * <<DataType>> Framework:: ExternalResource 35 metadata Descriptive, structured information about this event O 1 CharacterString 36 eventType Type of the event M 1 <<Codelist>> EventType 37 dataType Data type for the information stored in event value M 1 <<DataType>> Framework::DataType 38 eventValue Value being associated with the event M 1 CharacterString 39 location 

Geometric location of event that is not dependent on related feature location 

O 1 <<Union>> ElementGeometry 

40 measure 

Associated calculated measurements of length, height, and area 

O * Measurement 

41 attribute Extended unofficial attribute O * 

<<DataType>> Framework:: ExtendedAttribute 

42 Role name: feature Identity of the feature(s) on which this event occurs M * <<Abstract>> HydroFeature 43 ElementGeometry The geometry of a feature <<Union>> 44 polygon Bounded surface M 1 <<Type>> GM_Surface 45 point 0-dimensional geometric primitive representing a position [ISO 19107] M 1 <<Type>> GM_Point 46 line M 1 <<Type>> GM_Curve 
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6.2.7 MeasuredEvent A MeasuredEvent represents a point or span along a linear feature. In order to have MeasuredEvents, a linear feature 

linear reference model. A MeasuredEvent always has a StartMeasure and, if it represents a span along a feature, it al

The measures specifies the exact location of the event relative to the addresses/measures along the referenced feature. 

also have a geometric representation (inherits “location”) which provides an independent location for the event. Meproperties from the parent class, Event. These properties are not shown in the table below. 

Table 7 – Data dictionary for MeasuredEvent 

Line Name/Role Name Definition Obligation/ Condition Maximum Occurrence Data Type 

47 MeasuredEvent 

Property occuring at a point or along a span of one or more linear features 

<<Feature>> 

48 startPosition Measure along linear feature at which the measured event begins M 1 <<Type>> LinearReferenceSystem

LR_PositionExpression 

49 endPosition Measure along linear feature at which the measured event ends C/mandatory for EventType = Linear 1 <<Type>> LinearReferenceSystem

LR_PositionExpression 

50 startOffset 

Offset distance in current SRS units perpendicular to a linear feature where event starting point begins. Positive offsets are to the right of the feature looking upstream 

O 1 

<<Type>> LinearReferenceSystemLR_OffsetExpression 

51 endOffset 

Offset distance in current SRS units perpendicular to a linear feature ending point 

O 1 

<<Type>> LinearReferenceSystemLR_OffsetExpression 
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6.2.8 UnmeasuredEvent The UnmeasuredEvent may be linked to any feature that does not participate in the linear reference model. The referezero-dimensional, one-dimensional, or two-dimensional feature and may be either an HydroElement or HUnmeasuredEvents must have a location (geometry) that specifies the location of the event independent of the geom

feature. The geometry may be of point, line, or polygon as declared in the ElementGeometry Union class. Unmeproperties from the parent class, Event. These properties are not shown in the table below. 

Table 8 – Data dictionary for UnmeasuredEvent 

Line Name/Role Name Definition Obligation/ Condition Maximum Occurrence Data Type 

52 UnmeasuredEvent Event occuring on non-networked features <<Feature>> 53 location 

Geometric location of event that is not dependent on related feature location 

M 1 <<Union>> ElementGeometry 

54 ElementGeometry The geometry of a feature <<Union>> 55 polygon Bounded surface M 1 <<Type>> GM_Surface 56 point 0-dimensional geometric primitive representing a position [ISO 19107] M 1 <<Type>> GM_Point 57 line M 1 <<Type>> GM_Curve 
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6.2.9 Name The Name object holds feature names that are managed by a naming authority. The authority may be a recognized autho

Geographic Names or an un-recognized authority such as a local hydrography maintainer. An ExchangeCollection m

different authorities. Feature names are linked to HydroFeatures, both HydroElement and HydroComplex, in a many-to-

permits a given feature to have names from different authorities. It also permits a single name to be linked to Hydrrepresent parts of a named feature. 

Table 9 – Data dictionary for Name 

Line Name/Role Name Definition Obligation/ Condition Maximum Occurrence Data Type 

58 Name Name and identifier construct within 

a namespace <<DataType>> 

59 name Text name of the feature M 1 CharacterString 60 nameID Identifier and naming authority O 1 <<DataType>> Framework::Identifier 

6.2.10 Representation HydroFeatures, both HydroElement and HydroComplex, will have more than one representation in the hydrography comm

is one instance combination of feature attributes and geometry – variation in one characteristic constitutes a new HydroFeature instance within a given ExchangeCollection will have a single representation and the Representation representation is being exchanged. If the ExchangeCollection contains more than one representation for a given Hydrofeature instance (with unique identifier) for each representation in the ExchangeCollection. 

Table 10 – Data dictionary for Representation 

Line Name/Role Name Definition Obligation/ Condition Maximum Occurrence Data Type 

61 Representation Identification of geometric representation used <<DataType>> 62 representationID Unique identifier for the representation M 1 <<DataType>> Framework::Identifier 
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6.2.11 Measurement Measurement is used to store empirical measurements of features such as real-world reported elevation, length, area, values portrayed on topographical maps. HydroElement, HydroComplex, and Event features may have one or more Repo

Table 11 – Data dictionary for Measurement 

Line Name/Role Name Definition Obligation/ Condition Maximum Occurrence Data Type 

63 Measurement 

Reported area, length, depth, elevation, or height of hydrographic feature 

<<DataType>> 

64 accuracy Textual accuracy statement of the area measurement O 1 CharacterString 65 reportingOrganization Identity of the party reporting the measurement M 1 <<DataType>> ISO19115:: ResponsibleParty 66 units Code describing the parameter and units of measure M 1 <<CodeList>> UnitsType 67 value Value of the reported measurement M 1 CharacterString 
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6.2.12 ComputedNetworkValues The National Hydro Dataset (NHD) includes a number of computed values for hydrographic features (HydroElements) These properties are only calculated for features that participate in the network for which flow direction is known or inferred

Table 12 – Data dictionary for ComputedNetworkValues 

Line Name/Role Name Definition Obligation/ Condition Maximum Occurrence Data Typ

68 ComputedNetworkValues 

Group of computed values for features participating in the flow network 

* <<DataType>

69 fromNode 

Nationally unique ID for the “from” node (upstream node) endpoint 

C/computed 1 Integer 

70 toNode 

Nationally unique ID for the “to” node (downstream node) endpoint 

C/computed 1 Integer 

71 hydrologicSequenceNumber Nationally unique sequence number for the current reach C/computed 1 Integer 72 startFlag Code to mark headwater features C/computed 1 Integer 73 terminalFlag 

Code to mark features that terminate in the ocean, the Great Lakes, Canada, Mexico or in closed basins 

C/computed 1 Integer 

74 terminalDrainId 

Hydrologic sequence number for the terminal reach to which this drain flows 

C/computed 1 Integer 

75 levelPathId 

Hydrologic sequence number of the most downstream reach that is on the same level path 

C/computed 1 Integer 
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Line Name/Role Name Definition Obligation/ Condition Maximum Occurrence Data Typ

76 arbolateSumKm 

Sum of the lengths, in kilometers, of all the reaches that drain to the downstream end of the current reach 

C/computed 1 Real 

77 pathLengthKm 

Distance from this reach’s downstream end to the terminal reach downstream end 

C/computed 1 Real 

78 thinner 

Ordinal value to allow selection of progressively more dense networks; least dense network is where thinner = 1 

C/computed 1 Integer 

79 divergenceFlag Code signifying if reach is part of a flow divergence C/computed 1 Integer 80 drainStreamLevel 

Current stream level; supports upstream mainstream navigation 

C/computed 1 Integer 

81 downstreamDrainLevel 

Stream level of downstream mainstem reach; supports downstream navigation 

C/computed 1 Integer 

82 streamOrder Strahler stream order number for the reach C/computed 1 Integer 83 upstreamLevelPathId 

Level path identifier of the immediately upstream mainstem reach; supports navigation traversals through SQL queries 

C/computed 1 Integer 

84 upstreamHydrologicSequenceNumber 

Hydrologic sequence number of the immediately upstream mainstem 

C/computed 1 Integer 
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Line Name/Role Name Definition Obligation/ Condition Maximum Occurrence Data Typ

85 upstreamMinimumHydrologicSequenceNumber 

Minimum hydrologic sequence number of all immediately upstream reaches 

C/computed 1 Integer 

86 downstreamLevelPathId Level path identifier of downstream reach C/computed 1 Integer 87 downstreamDrainCount Number of drains immediately downstream C/computed 1 Integer 88 downstreamMinorHydrologicSequenceNumber 

At a divergence, the Hydrologic Sequence Number of the immediately downstream minor path reach 

C/computed 1 Integer 
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6.2.13 Common framework classes 

Three classes are shown in Figure 1 that are included from the Base Document (Part 0) for 

completeness. These classes are ExtendedAttribute, Identifier, and ExternalResource. The 

ExtendedAttribute object, described in Part 0, provides the ability to link additional attributes to 

HydroFeature instances, both HydroElement and HydroComplex. The ExtendedAttribute must 

have an authority which is documented with an authority (ISO19115::ResponsibleParty). The 

ExtendedAttribute may be documented through a URL to an ExternalResource object instance. 

The fuller description of this behavior is provided in the Part 0 but the classes are only shown 

here for convenience. 

The ExternalResource object provides the ability to link Internet URLs to HydroFeatures, both 

HydroElement and HydroComplex, to Events, to ISO19115::ResponsibleParty, and to 

ExtendedAttributes. There are a number of different types of ExternalResources as enumerated 

in the ResourceType code list. 

Identifier stores a set of related properties required for the management of information within a 

namespace. The identifier, a description, and a reference to an assigning authority are provided. 

The ResponsibleParty class comes from the ISO 19115 metadata concept of the same name but 

is implemented here to simplify the possible associations and recursion in the data model. 

ISO19115::ResponsibleParty provides descriptive details of an organization to which one can go 

and get additional contextual information. 

6.2.14 External packages 

Several UML packages of structured information are used or referenced from ISO sources in this 

part of the standard. These include geometry and linear referencing constructs from other ISO 

standards (GM_Object from ISO19107, CharacterString and Date from ISO/TS 19103). The 

inclusion of these packages of information complements the model. 

6.2.15 Code lists and enumerations 

The code lists presented in Figure 2 represent known values that are encouraged to promote 

interoperability. Code lists, by their nature are not closed enumerations and are not intended to 

be exhaustive. In fact, they might be placed online and would support controlled update by the 

community. In implementation, strict validation may include tests for the presence of these 

codes, whereas lax validation may permit these and additional code values. 
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cd Context Diagram: Hydro codelists and enumerations

«CodeList»

CompositeType

+ NHDReach

+ watercourse

«Enumeration»

Flow Code

+ bidirectional = 4

+ flowsOpposite = 2

+ flowsWith = 1

+ notApplicable = 0

+ unknown = 3

«CodeList»

Ev entType

+ bay/inlet

+ bridge

+ crevasseField

+ ephemerality

+ rapids

+ tunnel

+ waterfall

«CodeList»

UnitsType

+ reportedAreaHectares

+ reportedAreaKm

+ reportedAreaSqmi

+ reportedElevationFeet

+ reportedElevationMeters

+ reportedLengthFeet

+ reportedLengthMeters

«CodeList»

RelationshipType

+ flowsTo

+ overpasses

«CodeList»

HydroFeatureType

+ areaOfComplexChannels

+ areaToBeSubmerged

+ artificialPath

+ canalDitch

+ coastline

+ connector

+ damWeir

+ estuary

+ flume

+ gate

+ iceMass

+ inundationArea

+ lakePond

+ lockChamber

+ pipeline

+ reservoir

+ seaOcean

+ shoreline

+ sinkRise

+ spillway

+ springSeep

+ streamRiver

+ swampMarsh

+ waterIntakeOutflow

+ well

«Type»

Linear Reference Systems::

LR_PositionExpression

+ measure: Measure

«Type»

Linear Reference Systems::

LR_OffsetExpression

{root,leaf}

+ offset[0..1]: Measure

+ offsetReference: LR_OffsetReference

«Type»

Linear Reference Systems::

LR_LinearReferenceMethod

{root,leaf}

+ name: CharacterString

+ offsetUnits: UnitOfMeasure

+ positiveOffsetDirection: LR_OffsetDirection = "right"

+ type: CharacterString

+ units: UnitOfMeasure

+ project(GM_Point*) : LR_PositionExpression

«Enumeration»

Linear Reference 

Systems::

LR_OffsetDirection

{root,leaf}

+ above

+ below

+ left

+ right

«CodeList»

Linear Reference 

Systems::

LR_OffsetReference

{root,leaf}

+ centerline

+ curb

+ edgeOfBerm

+ edgeOfTravel

+ rightOfWay

+ sidewalkInside

+ sidewalkOutside

+LRM

1

+offset 0..1

Figure 2 – Hydrography UML class code lists and enumerations 
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6.3 Example hydrography data 

Figure 3 below represents a small collection of hydrography features, their attributes, and 

relationships. Only selected characteristics are shown to illustrate a basic network of 

hydrographic features. These notional representations can be translated into the logical UML 

model as well as implementation models such as relational databases. 

Figure 3 – Example basic hydrographic data 
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Part 6: Hydrography 

Annex A (normative): Feature codes, code lists, and enumerations

23

Annex A 

(normative) 

Feature codes, code lists, and enumerations 

A.1 Common hydrography feature and feature codes 

The following table includes common coded combinations of properties, or feature codes, 

associated with hydrographic features as used in the National Hydrography Dataset. These 

codes are intended to simplify association and classification of features for applications and 

symbology. A hydrography feature code is the numeric value used that encodes the unique 

combination of hydrography feature type and a set of feature attribute values. The official fivedigit hydrography feature code has two parts: the first three digits encode the feature type; the 

last two digits encode values for a set of attributes associated with the feature. 

Table A.1 – Common feature codes 

FCode Description 

53700 Area of Complex Channels 

30700 Area to be Submerged 

55800 Artificial Path 

33600 Canal/Ditch 

33601 Canal/Ditch: Canal/Ditch Type = Aqueduct 

56600 Coastline 

33400 Connector 

34300 Dam/Weir 

34305 Dam/Weir: Construction Material = Earthen 

34306 Dam/Weir: Construction Material = Nonearthen 

49300 Estuary 

36200 Flume 

36900 Gate 

37800 Ice Mass 

40300 Inundation Area 

40308 Inundation Area: Inundation Control Status = Controlled 

40309 Inundation Area: Inundation Control Status = Controlled; Stage = Flood Elevation 

40307 Inundation Area: Inundation Control Status = Not Controlled 

39000 Lake/Pond 

39001 Lake/Pond: Hydrographic Category = Intermittent 

39006 Lake/Pond: Hydrographic Category = Intermittent; Stage = Date of Photography 
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FCode Description 

39005 Lake/Pond: Hydrographic Category = Intermittent; Stage = High Water Elevation 

39004 Lake/Pond: Hydrographic Category = Perennial 

39009 Lake/Pond: Hydrographic Category = Perennial; Stage = Average Water Elevation 

39011 Lake/Pond: Hydrographic Category = Perennial; Stage = Date of Photography 

39010 Lake/Pond: Hydrographic Category = Perennial; Stage = Normal Pool 

39012 Lake/Pond: Hydrographic Category = Perennial; Stage = Spillway Elevation 

39800 Lock Chamber 

42800 Pipeline 

42816 Pipeline: Pipeline Type = Aqueduct 

42801 Pipeline: Pipeline Type = Aqueduct; Relationship to Surface = At or Near 

42802 Pipeline: Pipeline Type = Aqueduct; Relationship to Surface = Elevated 

42803 Pipeline: Pipeline Type = Aqueduct; Relationship to Surface = Underground 

42804 Pipeline: Pipeline Type = Aqueduct; Relationship to Surface = Underwater 

42814 Pipeline: Pipeline Type = General Case 

42805 Pipeline: Pipeline Type = General Case; Relationship to Surface = At or Near 

42806 Pipeline: Pipeline Type = General Case; Relationship to Surface = Elevated 

42807 Pipeline: Pipeline Type = General Case; Relationship to Surface = Underground 

42808 Pipeline: Pipeline Type = General Case; Relationship to Surface = Underwater 

42815 Pipeline: Pipeline Type = Penstock 

42809 Pipeline: Pipeline Type = Penstock; Relationship to Surface = At or Near 

42810 Pipeline: Pipeline Type = Penstock; Relationship to Surface = Elevated 

42811 Pipeline: Pipeline Type = Penstock; Relationship to Surface = Underground 

42812 Pipeline: Pipeline Type = Penstock; Relationship to Surface = Underwater 

42813 Pipeline: Pipeline Type = Siphon 

43600 Reservoir 

43618 Reservoir: Construction Material = Earthen 

43619 Reservoir: Construction Material = Nonearthen 

43601 Reservoir: Reservoir Type = Aquaculture 

43609 Reservoir: Reservoir Type = Cooling Pond 

43603 Reservoir: Reservoir Type = Decorative Pool 

43606 Reservoir: Reservoir Type = Disposal 
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Annex A (normative): Feature codes, code lists, and enumerations

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FCode Description 

43625 Reservoir: Reservoir Type = Disposal; Construction Material = Earthen 

43626 Reservoir: Reservoir Type = Disposal; Construction Material = Nonearthen 

43607 Reservoir: Reservoir Type = Evaporator 

43623 Reservoir: Reservoir Type = Evaporator; Construction Material = Earthen 

43610 Reservoir: Reservoir Type = Filtration Pond 

43611 Reservoir: Reservoir Type = Settling Pond 

43612 Reservoir: Reservoir Type = Sewage Treatment Pond 

43608 Reservoir: Reservoir Type = Swimming Pool 

43605 Reservoir: Reservoir Type = Tailings Pond 

43604 Reservoir: Reservoir Type = Tailings Pond; Construction Material = Earthen 

43617 Reservoir: Reservoir Type = Water Storage 

43613 Reservoir: Reservoir Type = Water Storage; Construction Material = Nonearthen 

43614 Reservoir: Reservoir Type = Water Storage; Construction Material = Earthen; Hydrographic Category = 

Intermittent 

43615 Reservoir: Reservoir Type = Water Storage; Construction Material = Earthen; Hydrographic Category = 

Perennial 

43621 Reservoir: Reservoir Type = Water Storage; Hydrographic Category = Perennial 

43624 Reservoir; Reservoir Type = Treatment 

44500 Sea/Ocean 

56700 Shoreline 

45000 Sink/Rise 

45500 Spillway 

45800 Spring/Seep 

46000 Stream/River 

46003 Stream/River: Hydrographic Category = Intermittent 

46006 Stream/River: Hydrographic Category = Perennial 

46600 Swamp/Marsh 

48500 Water Intake/Outflow 

48800 Well 
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A.2 Feature code lists and enumerations A.2.1 General The following tables represent consolidated code lists and enumerations of recognized feature types for water features. non-water features were omitted from this list. Where possible, potential or identified alternate names (aliases) consolidation occurred where what used to be a feature type was recognized to be, in fact, a modifier or property on somthese cases, the column of “characteristics” reflects possible modifiers. A.2.2 Feature code lists 

A.2.2.1 CompositeType code list 

CompositeType is a CodeList of values for the attribute compositeType. 

Table A.2 – CodeList for CompositeType 

Value Name Feature Name Definition Characteristics 

NHDReach NHDReach 

A complex feature that is scale-independent and carries a publicly recognized permanent identifier [USGS] 

watercourse Watercourse 

A HydroComplex feature, made up of one or more features usually based on a name attribute [USGS] 

A.2.2.2 EventType code list 

In the NHD, the contact between land and coastal features is captured as Coastline. The NHD does not support the shor

shorelines could be derived for the purpose of exchange from existing bounded water area features. The provision of shother feature type) is not mandatory, but supported by the Hydrography part of the Framework Data Content Standard. 

• Bridges and tunnels are properties of canal/ditches and pipelines 

• Crevasse field is an attribute of an ice mass • Foreshores are the area between high and low water but are problematic. Should really be defined by NOAA c

derivable 
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• Hazard zone is a property of general water features, not a first order feature • Islands are not water features but may be landmark features. Out of scope in this part but may be supported in so• A Reach is not a first-order feature but rather is a characteristic (Reach identity) used to group kindred feature ins

may consider a replacement term for “reach” 

• Sand and gravel bar is more like an island and is excluded • Sounding datum line (tidal datum) is like edge of foreshore. It seems out of context 

• Special use zone and special use zone limit are really properties of any area water feature. These are not show

type table, above, but may be revealed in the FCODE enumeration 

EventType is a CodeList of values for the attribute eventType. 

Table A.3 – CodeList for EventType 

Value Name Characteristic Definition Referenc

bay/inlet Bay/Inlet 

A water area that is an opening of the sea/ocean into the land, or of an estuary, lake, or river into its shore. (Implemented as a landmark feature) [USGS] 

Estuary, Lake/PSea/Ocean, St

bridge Bridge 

Structure spanning and providing passage over a waterway, railroad or other obstacle. For example, a characteristic of a canal/ditch or pipeline with passage over a stream [USGS] 

Canal/Ditch, Pi

crevasseField Crevasse Field Area of deep fissures in the surface of an ice mass caused by breaking or parting [USGS] Ice mass ephemerality Ephemerality The perennial or intermittent nature of a flowing water feature [USGS] Lake/Pond, Strrapids Rapids 

An area of swift current in a stream or river, characterized by standing waves or by boulders and rocks [USGS] 

Stream/River 

tunnel Tunnel An underground or underwater passage [USGS] Canal/Ditch, Piwaterfall Waterfall A vertical or near vertical descent of water over a step or ledge in the bed of a river [USGS] Stream/River 
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A.2.2.3 HydroFeatureType code list 

HydroFeatureType is a CodeList of values for the attribute featureType. 

Table A.4 – CodeList for HydroFeatureType 

Value Name Feature Name Definition Code Characteristics 

areaOfComplexChannels Area of Complex Channels 

An area where a stream or river flows in an intricate network of interlacing channels [USGS] 

537 

areaToBeSubmerged Area to be Submerged 

The known extent of the intended lake that will be created behind a dam under construction [USGS] 

307 

artificialPath Artificial path 

An abstraction to facilitate hydrologic modeling through open water bodies and along coastal and Great Lakes shorelines and to act as a surrogate for lakes and other water bodies [USGS] 

558 

canalDitch Canal/Ditch 

An artificial open waterway constructed to transport water, to irrigate or drain land, to connect two or more bodies of water, or to serve as a waterway for watercraft [USGS] 

336 Tunnel Aqued

 Coastline 

The contact line between land and water along the Atlantic, Pacific, or Arctic Oceans, the Great Lakes, the Gulf of Mexico, or the Caribbean Sea [USGS] 

566 
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Value Name Feature Name Definition Code Characteristics 

connector Connector 

A known, but nonspecific, connection between two nonadjacent network segments [USGS] 

334 

damWeir Dam/Weir 

A barrier constructed to control the flow or raise the level of water [USGS] 

343 Levee 

estuary Estuary 

The lower end of a river, or a semienclosed coastal body of water with access to the open ocean, which is affected by the tides and where fresh and salt water mix. Should be hydrologically based [USGS] 

493 Bay 

flume Flume 

An open, inclined, artificial channel constructed of wood, metal, or concrete; generally elevated [USGS] 

362 

gate Gate 

A structure that may be swung, drawn, or lowered to block an entrance or passageway [USGS] 

369 

iceMass Ice Mass 

A field of ice, formed in regions of perennial frost [USGS] 

378 Crevasse Field Glacie

inundationArea Inundation Area An area of land subject to flooding [USGS] 403 lakePond Lake/Pond 

A standing body of water with a nearly horizontal water surface and a predominantly natural shoreline surrounded by land. May be natural or formed by a dam/weir [USGS] 

390 Gravel Pit/Quarry, Playa 
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Value Name Feature Name Definition Code Characteristics 

lockChamber Lock Chamber 

An enclosure on a waterway used to raise and lower vessels as they pass from one level to another [USGS] 

398 

pipeline Pipeline 

A closed conduit, with pumps, valves and control devices, for conveying fluids, gases, or finely divided solids [USGS] 

428 

Aqueduct (if closed), Siphon, Tunnel 

reservoir Reservoir 

A constructed basin formed to contain water or other liquids [USGS] 

436 

seaOcean Sea/Ocean 

The great body of salt water that covers much of the Earth [USGS] 

445 Gulf 

shoreline Shoreline 

The contact line between land and an inland waterbody [USGS] 

567 

Coastal, Island, Reservoir, Nonearthen, Stream/River 

sinkRise Sink/Rise 

The place at which a stream disappears underground or reappears at the surface in a karst area [USGS] 

450 

spillway Spillway 

A constructed passage for surplus water to run over or around a dam [USGS] 

455 Maso

springSeep Spring/Seep 

A place where water issues from the ground naturally [USGS] 

458 Mudpot, Fumarole, Geyser 

streamRiver Stream/River A body of flowing water [USGS] 460 Wash Ephe
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Value Name Feature Name Definition Code Characteristics 

swampMarsh Swamp/Marsh 

A (generally) noncultivated, vegetated area that is inundated or saturated for a significant part of the year. The vegetation is adapted for life in saturated soil conditions [USGS] 

466 Bog, W

waterIntakeOutflow Water Intake/Outflow 

A structure through which water enters or exits a conduit [USGS] 

485 Intake, Outflow 

well Well 

A pit or hole dug or bored into the earth for the extraction of water [USGS] 

488 
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A.2.2.4 RelationshipType code list 

RelationshipType is a CodeList of values for the attribute type. 

Table A.5 – CodeList for RelationshipType 

Name Definition 

flowsTo Downstream association between the first, or 'from' feature to the second, 

or “to” feature 

overpass Relationship between features where the first feature overpasses the 

second feature such that the water flows do not combine 

A.2.2.5 UnitsType code list 

UnitsType is a CodeList of values for the attribute units. 

Table A.6 – CodeList for UnitsType 

Name Definition 

reportedAreaHectares Area in hectares 

reportedAreaKm Area in square kilometers 

reportedAreaSqmi Area in square miles 

reportedElevationFeet Elevation above sea level expressed in feet 

reportedElevationMeters Elevation above sea level expressed in meters 

reportedLengthFeet Length reported in feet 

reportedLengthMeters Length reported in meters 

A.2.3 FlowCode enumeration 

FlowCode is an enumeration of values for the attribute flowDirection. 

Table A.7 – FlowCode enumeration 

Name Definition 

notApplicable (0) Flow inference not applicable to the feature, e.g. shoreline 

flowsWith (1) Flow of water is the same direction as coordinate order 

flowsOpposite (2) Flow of water is the opposite direction of coordinate order 

unknown (3) Flow direction of water unknown 

bidirectionsal (4) Water may flow either direction along feature 
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Part 6: Hydrography 

Annex B (informative): Design concepts and design requirements

33

Annex B 

(informative) 

Design concepts and design requirements 

B.1 Design concepts 

Several key design concepts are defined in the Hydrography part, as defined by requirements of 

water resource applications: 

• Core component of this part and model is the feature 

• All features have geometry, either directly or through association 

• Features are classified by type and further qualified by attributes 

• Features may have relationships to other features 

• Common definition of features is required for data sharing 

• Permanent identifiers on features and on associated data are managed by an authority 

• Linear referencing is supported through permanent features, identifiers, and 

measurement references 

• Multiple representations of a feature exist and are managed in a community 

B.2 Design requirements 

Hydrographic applications have specific data and information needs associated with them. Below 

is a table of examples of such requirements. 

Table B.1 – Design requirements 

Uses Data and Information Needed 

Trace pollution upstream and downstream 

Permanent features with IDs, information on flow of water 

through surface water network, feature classification, 

measurements on the surface water network, water 

discharge and velocity 

Assist recovery of threatened and endangered species 

Permanent features with IDs, linear reference system, 

surface water flow relationships, measurements on the 

surface water network 

Identify withdrawn areas for timber harvesting based on 

riparian and stream characteristics 

Shoreline, surface water flow relationships, linear reference 

system, measurements on the surface water network, 

feature classification 

Make maps as a reference layer with other data Feature names, feature classification, attributes for 

generalizing or symbolization 

Landscape analysis: influence of hydrography on landscape 

and vice versa 

Flow relationships, history of features, positional accuracy, 

quality information, feature classification 

Emergency management system for displaying impact 

areas and model flooding Permanent features with identifiers (identifies), watersheds 

Display and identify the identities/names of water features at 

a location Features, IDs, names, geometries 

Update local data with most up-to-date hydrography Permanent feature IDs, representation IDs, metadata 
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Part 6: Hydrography 

Annex B (informative): Design concepts and design requirements

34

Based on these requirements, this part and model support the concepts described in the data and 

information needs. 

Features are central to the hydrography model. Other data objects exist in the model through 

association to the features. A HydroElement feature is a geographic entity that can be classified 

by consistent type over its extent. A HydroComplex feature is an aggregation of HydroElement 

features. 

This part of the Framework Data Content Standard contains specific feature classifications so that 

all exchange datasets that conform to it are consistent in terms of form or function, and in terms 

of minimum attributes of those features. For example, if one creates an exchange dataset 

according to this part and if that exchange dataset contains features classified as “stream”, then 

those features would meet the part’s definition of a “stream”. This part contains feature type 

enumerations and associated specific definitions that represent a set of harmonized types from 

major stakeholder systems. 

Additional classification qualifiers are captured as attributes, also with specific definitions and, 

where appropriate, with code lists. The code lists should not be considered as bounded – more 

like an open-ended list – but that these types are the currently recognized ones for information 

exchange. Different provider-consumer arrangements might require validation against this list, or 

permit exchange of extended and non-standard feature types. 

Characteristics that are less fixed to a permanent location on the ground should not "break" 

features, but be linked to the core data so as to remain accessible. For example, an application 

of name is concrete and can be tied explicitly to the feature. However, a classification of 

hydrographic category (for example, intermittent versus perennial) is less fixed and may be better 

represented though a time series or a statistical measure, but not by explicit points that "break" 

the underlying feature. 

As a Framework Data Content Standard, the hydrography model emphasizes permanent features 

with unique permanent IDs to support the community’s uses of hydrography data. Permanent 

identifiers allow sharing of data in a distributed environment. Permanent identifiers are required 

to support maintaining entities over time (for example, exchange of updates); to support 

maintaining entities across multiple representations (for example, scale and/or dimension); to 

support maintaining associations to linked data; and to describe associations among local and 

external data entities, such as water quality or ecological surveys. 

Any permanent identifier scheme requires an authority to manage the included features.1

 The 

model also allows assignment of local identifiers to server as temporary identifiers or as crosswalks to permanent identifiers. If a permanent identifier does not exist, the model requires at 

least a unique temporary identifier be assigned for the purpose of the exchange. All feature 

identifiers must be unique in the context of the transfer and within an authority’s coding system. 

The responsibilities of an authority include: recognition as a maintenance authority within the 

community, ability to assign, update, manage and publish identifiers, and to assure that identifiers 

are discoverable by users within a reasonable timeframe of their registration. 

This part of the standard supports the management of multiple representations of features. A 

feature instance may have multiple representations reflecting different geometries and attributes 

due to changes over time, changes in scale, or differing generalization criteria applied in support 

of user needs. This part does not define a “best available” spatial representation since these 

differ depending on the application of the data. Data authorities may establish specific data 

capture requirements to data under their authority. Some feature types, such as reaches and 

watercourses, do not have direct spatial representation, but instead derive their geographic extent 

 

1

 Recognized authorities include the National Hydrography Dataset co-administered by the U.S. Geological Survey and 

the U.S. Environmental Protection Agency, and the U.S. Geographic Names Information System in which official 

place names are stored. Both authorities support unique and persistent identifiers for features under their 

maintenance. 
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Part 6: Hydrography 

Annex B (informative): Design concepts and design requirements

35

through association to other feature types that do have spatial representation. A feature extent is 

defined by stable characteristics that allow for distinct bounds (for example, start, end, location, 

extent) of the feature instance. 

The combination of a specific instance of a feature – all its attributes including a specific geometry 

– can be identified with a unique representation identifier. Thus a representation identifier 

denotes a unique, identifiable packaging of a feature, its attributes, and its geometry. This 

representation identifier provides a unique code to identify the state of the described feature. For 

example, a change in attribution or geometry preserves the same permanent feature identifier for 

purposes of linking to references or tracking changes, but would be tagged with a new 

representation identifier to indicate a change in the representation. When there are multiple 

persistent representations of a feature, such as those based on scale, then each representation 

would have its own identifier. Representation identifiers should be derived algorithmically, 

applying methods like a checksum from attributes and geometry or assignment of truly universally 

unique identifiers (UUID) or globally unique identifiers (GUID). 

Features may have relationships to other features to describe connectivity or association. 

Relationship types include flow behavior, vertical offsets, and composition. The feature members 

of the relationship are referenced through their identifiers. The flow connectivity described in 

these relationships supports development of a linear flow network for flow navigation without the 

use of geometry. An attribute should be specified to note whether flow direction is one-way, bidirectional, or unknown. The endpoints of segments (nodes, junctions) will not be managed as 

first order features in this model. 

Hydrography features are classified as either elemental (HydroElement) or complex 

(HydroComplex). HydroElement features, as enumerated in the Annex on HydroFeatureTypes, 

are of a particular feature type that has geometry and may have attributes, relationships, and 

events. HydroComplex features exist only as aggregations of HydroElement features and do not 

have their own explicit geometry. Examples of HydroComplex features are “reach” and named 

“watercourse”. HydroElement features may not be composed of other HydroElement features. 

HydroComplex features may be composed of only one set of HydroElement features; for 

simplicity, the composition relationship is not recursive. 

This part of the standard supports a continuous linear representation of the surface water 

network, although it permits the management and exchange of non-networked features. The 

network is composed of features that are represented as line strings whose connectivity 

relationship is known. The logical network is composed of linear representations of hydrography 

features and centerlines (artificially derived flow paths) within area representations such as 

reservoirs, rivers, and lakes. A “flows-through” relationship exists between centerlines and the 

area feature representations through which they flow. The geometric representation of features 

supported by this part of the standard includes point, line, and area representations only 

(GM_Point, GM_Curve, GM_Surface). 

The Hydrography part contains a reference system that supports both linear and non-linear links 

to the hydrography data. The reference system is described by a single type of HydroComplex 

features (for example, reaches or watercourses). The reference system features have an 

attribute that can be used as the reference key. The reference key attribute contains unique 

values. External information that is linked to the reference system does so by referring to the 

reference key. The reference systems features may have any configuration of geometry: point, 

line, or area. The reference system's linear features may support a linear reference system. The 

features that make up the linear reference system have an attribute that identifies the features as 

being part of a linear reference system. Addresses or measures are assigned along the linear 

features to support linking external information to just a portion of a linear feature. The addresses 

or measures begin with zero (0) at one end of the feature and terminate with one-hundred (100) 

at the other end of the feature. Measures are applied to linear features in proportion to their 

length. The reference system is defined on HydroComplex features, therefore the measures are 

designated based on the HydroComplex Feature's consolidated geometry which it inherits from 
Federal Geographic Data Committee FGDC-STD-014.6-2008 

Geographic Information Framework Data Content Standard 

Part 6: Hydrography 

Annex B (informative): Design concepts and design requirements

36

its HydroElement features. The measures are stored on the geometry of the HydroElement 

features as a measure (that is to say, “m”) value for each geometry coordinate. The coordinates 

of linear features in the reference system are ordered from upstream to downstream if the 

direction of flow is known. Measurements increase in the opposite direction of the coordinate 

order. Therefore, by definition, where direction of flow is known, measure values increase from 

downstream to upstream. Both linear and non-linear references support an event model whereby 

the events are associated to the feature through its reference key and, optionally, to locations 

along the feature defined by the feature's measures. Measurements along shorelines should 

have a well-known starting location, such as the point of major outflow or other reference point. 

Management of feature names is a core requirement for the Hydrography part, including the 

ability to manage multiple names of the same feature in an exchange. Names are provided in the 

context of a naming authority, such as the GNIS. To differentiate among different named features 

that are identically named – for example, all the “Mill Creeks” – a unique identifier is assigned by 

an authority to each named feature instance. 

Metadata can be managed for the entire data exchange collection (feature collection), for a 

feature, or for an event. Although either FGDC or ISO 19115 metadata can be associated with 

these hydrography data, ISO 19115 is especially suited to describing characteristics on 

collections, datasets, and features. This part of the Framework Data Content Standard requires 

data history/lineage to be reported in metadata so users understand the context for data 

exchanged. It does not impose constraints on metadata; it requires that metadata be reported 

using FGDC or ISO 19115 schemes as part of the data transfer. 
Federal Geographic Data Committee FGDC-STD-014.6-2008 

Geographic Information Framework Data Content Standard 

Part 6: Hydrography 

Annex C (informative): Bibliography

37

Annex C 

(informative) 

Bibliography 

The following documents contain provisions that are relevant to this part of the Framework Data 

Content Standard. Annex D of the Base Document (Part 0) lists informative references 

applicable to two or more of the parts of the standard. For dated references, only the edition cited 

applies. For undated references, the latest edition of the referenced document applies. 

ANSI and ISO standards may be purchased through the ANSI eStandards Store at 

http://webstore.ansi.org/ansidocstore/default.asp, accessed October 2006. 

ESRI, ArcHydro data model 

U.S. Board on Geographic Names, Geographic names information system, 

http://geonames.usgs.gov/bgn.html, accessed October 2006 

U.S. Geological Survey, 1999, Standards for national hydrography dataset (Draft), 

http://rockyweb.cr.usgs.gov/nmpstds/nhdstds.html, accessed October 2006 

Washington and Oregon Hydrography Framework Technical Work Groups, 2004, Pacific 

northwest framework, http://hydro.reo.gov/docs.html, accessed October 2006