PROJECT TITLE: National Hydrography Framework Data Model

DATE OF PROPOSAL: February 1, 2001

TYPE OF STANDARD PROPOSED: Data Content . Data Model

SUBMITTING ORGANIZATION: FGDC Subcommittee on Spatial Water Data (SSWD) {to be confirmed}

POINT OF CONTACT: Richard Hogan, U.S. Geological Survey, MS-511, 12201 Sunrise Valley Drive, Reston, VA 20192 (703) 648 5531 (rlhogan@usgs.gov)

OBJECTIVE: To establish a standard data model for encoding information about naturally occurring and constructed bodies of water, paths through which water flows, and related entities as currently implemented within the USEPA/USGS National Hydrography Dataset.

SCOPE: The model will include the identification of a basic set of features and attributes that make up a drainage system and the logical description of how these features and attributes will be represented in a nationally consistent framework data set. Key aspects of the data model will include the methodology for the unambiguous identification of "reaches", the basic spatial component of the system, and the methodology for assigning permanent, unique codes to reaches. The model will also include specific means for associating metadata to features and attributes defined by the model.

JUSTIFICATION/BENEFITS: The National Hydrography Dataset (NHD) is the culmination of cooperative efforts of the U.S. Environmental Protection Agency (USEPA) and the U.S. Geological Survey (USGS). Other organizations also contributed to the effort. The initial data set was implemented at a nominal scale of 1:100,000 and forms the basic framework. Over 30 states are currently working with USEPA and USGS to demonstrate how the data model supports the integration of higher resolution data into the basic framework. Standardizing the data model represented by the NHD at this time will encourage greater participation in the full multi-resolution implementation of this important framework data layer. It will also help stimulate the commercial development of hydrographic and hydrologic applications by providing a well-defined, stable, and widely used data model, which system developers can use to create standardized interfaces.

The NHD is a comprehensive set of digital spatial data that encodes information about naturally occurring and constructed bodies of water, paths through which water flows, and related entities. The information encoded about these features includes classification and other characteristics, delineation, geographic name, position and related measures, a "reach code" through which other information can be related to the NHD, and the direction of water flow. In addition to this geographic information, the dataset contains metadata and information that supports the exchange of future updates and improvements to the data.

The data support many applications, such as:

• Making maps. Positional and descriptive data in the NHD provide the starting point for making many different kinds of maps.
• Geocoding observations. Much like street addresses provide a way to link data to a road network, the NHD's "reach code" provides the means to link data to water features.
• Modeling the flow of water along the Nation's waterways. Information about the direction of flow, when combined with other data, can help users model the transport of materials in hydrographic networks, and other applications.
• Maintaining data. Many organizations would like to share the costs of improving and updating their collections of geographic data. Unique identifiers and other methods encoded in the NHD help to solve technical problems of cooperative data maintenance.

DEVELOPMENT APPROACH: The current documentation of the National Hydrography Dataset (volume 1, attached) will be used as the basic reference document for the development of the standard. The data model will be extracted and rewritten as a geographic information framework standard. To the extent possible the resulting data model will conform to the ISO 19100 series of abstract specifications being developed by ISO/TC 211, Geographic information/Geomatics.

The first step will be to use the Unified Modeling Language (UML) to describe the model consistent with the guidance of ISO 19103 . Conceptual schema language. Then features and attributes will be described using the methodology defined in ISO 19110 . Cataloguing methodology. Metadata will be defined consistent with the FGDC Content Standard of Digital Geospatial Metadata, but every effort will be made to also comply with ISO 19115 - Metadata. The resulting specification should meet the requirements for description of an application schema as defined in ISO 19109 . Rules for application schema. Members of the FGDC Standards Working Group who have participated in the work of ISO/TC 211 and are familiar with those standards and other interested parties will oversee this work.

RELATED STANDARDS:
The existing NHD data model has a known relationship to the following standards:

• FGDC-STD-001-1998 Content Standard for Digital Geospatial Metadata
  The metadata in the NHD is consistent with this standard
• ANSI/NCITS X3.145-1986 . Codes Identification of Hydrologic Units The "reach codes" in the NHD are based on the hydrologic unit codes found in this standard
• (FGDC Draft) Framework Transportation ID Standard
  This specification uses the same concept for modeling a network data structure and creating permanent feature IDs. The resulting specifications differ to the extent that hydrographic and transportation networks have differing characteristics. However, the concepts employed in creating the two specifications are the same.

The specification resulting from this standards project is expected to conform (to the extent possible) to the following emerging standards as described in the development approach above:

• ISO/CD 19103 . Conceptual schema language
• ISO/DIS 19107 . Spatial schema
• ISO/CD 19109 . Rules for application schema
• ISO/DIS 19110 . Cataloguing methodology
• ISO/DIS 19115 . Metadata

The resulting specification is also expected to have a relationship to the following standards, but the exact nature of that relationship is unknown at this time. The relationship will be determined during the development of the final specification. (FGDC Draft) Hydrographic Data Content Standard for Coastal and Inland Waterways (FGDC Draft) Metadata Profile for Shoreline Data

DEVELOPMENT AND COMPLETION SCHEDULE: TBD

RESOURCES REQUIRED: TBD

POTENTIAL PARTICIPANTS: SSWD members that have participated in the development of the NHD are potential participants, especially USGS and USEPA. Other FGDC subcommittee and working group members that are familiar with the ISO/TC 211 specifications are also potential partners.

OTHER TARGET AUTHORIZATION BODIES: NCITS L1 may want to consider all or part of this specification as a companion standard to X3.145. Assuming that this specification will conform to ISO/TC 211 general specifications for geographic information, this standard could be introduced in ISO/TC 211 as a standardized application schema