Digital Geospatial Metadata
Geospatial metadata commonly document geographic digital data resources such as Geographic Information System (GIS) files, geospatial databases, and earth imagery. But geospatial metadata can also be used to document geospatial resources that may include data catalogs, mapping applications, data models and related websites. Geodata refers to actual geographic data resources.
A metadata record is an information file that captures the basic characteristics of a geographic data or information resource, and represents the who, what, when, where, why and how of the geodata resource. Geospatial metadata records include:
- Core library catalog elements such as Title, Abstract, and Publication Data;
- Elements such as Geographic Extent and Projection Information; and
- Database elements such as Attribute Label Definitions and Attribute Domain Values.
The CGDI supports Catalogue Services for the Web (CSW) that contains metadata about geodata resources. A CSW identifies the agency that is responsible for each attribute dataset, with descriptions of that attribute data. CSWs also contain information on how to access the data.
Transition to the North American Profile
The original FGDC Content Standard for Digital Geospatial Metadata (CSDGM) provided a common set of terminology and definitions for the documentation of digital geospatial metadata, establishing the names of data elements and compound elements (groups of data elements) to be used for these purposes, the definitions of these data elements and compound elements, and the values to be provided for them.
The new North American Profile (NAP) of the ISO 19115: Geographic Information – Metadata is expected to replace the FGDC standard in the near future.
In the same way that the original FGDC-CSDGM codified geospatial data documentation for the geospatial data community, the NAP extends standardization across national borders. While the NAP does not include the same level of detail as the CSDGM, it does provide the following features:
- Fewer mandatory elements and more optional elements;
- Extended elements and new elements to capture more specific information;
- A hierarchical structure that creates ‘packages’ of metadata that can be reused and combined to form new metadata records;
- Support for the documentation of new geospatial data topologies and technologies including geo-databases, web mapping applications, data models, data portals, ontologies, etc.; and
- Suggested best practices for populating metadata elements in a manner that enhances the quality and usefulness of the metadata.
Often referred to as the “FGDC Metadata Standard”,
Efforts are underway to finalize a new national and international geospatial metadata standard - The North American Profile (NAP) of the ISO 19115: Geographic Information – Metadata.
Please check the OGC® and FDGC websites for the latest information about NAP implementation and resources.
Additional Information (Digital Geospatial Metadata)
Since it was introduced, the FGDC-CSDGM has been adopted by many organizations external to the U.S. federal government, in both the public and private sectors, and in other nations including Canada. The CSDGM is a valuable resource for documenting geospatial metadata in a standardized manner that facilitates discovery, access, use, and archiving. In addition, the standard has been used to document web-mapping applications, data-acquisition projects, data models, and other ‘non-traditional’ geospatial resources. As these new forms of geospatial resources evolve, new requirements for documentation have emerged.
In 1999 the ISO/TC 211 was tasked with harmonizing the CSDGM with other geospatial metadata standards and a range of de facto standards that had emerged to address new requirements for geospatial documentation. The result was the publication of ISO 19115: Geographic information – Metadata. Since then, a number of organizations and nations have developed implementation ‘profiles’ of the standard.
ISO 19115 is an abstract standard. It specifies the definition of elements and the relationship among elements but does not provide guidance as to how the content is organized into a formal record and presented to the reader. Without this critical component, the standard could not be promoted for implementation. A separate ISO/TC 211 effort, ISO 19139 - Geographic information -- Metadata -- XML schema implementation, was undertaken to provide an eXtensible Mark-up Language (XML) implementation schema to specify the ISO 19115 metadata record format and to support the description, validation, and exchange of geospatial metadata. Even with the XML schema under development, concerns remained as to the adequacy of ISO 19115 to meet the needs of the CSDGM community. One key concern was the lack of elements for the documentation of a geospatial database. Known as ‘Entities and Attributes’ within the CSDGM, TC 211 had designated the development of the database documentation elements to yet another separate standard, ISO 19110 - Methodology for Feature Cataloging.
It was not until the finalization of the ISO 19110 in 2005 and ISO 19139 in 2007, that the resources were in place to develop a profile of ISO 19115 that provided both the structure and content needed to support migration of CSDGM metadata to the international suite of geospatial metadata standards. The result is the North American Profile (NAP) of the ISO 19115: Geographic Information – Metadata. The NAP was developed to achieve the following objectives:
Support geographic data producers in their efforts to:
- maintain an inventory of geographic data and services,
- organize and manage geographic data and services, and
- publish information internationally about available geographic data and services.
Support geographic data consumers in their efforts to:
- discover and access needed geographic data and services internationally,
- assess the fitness for use of available geographic data and services, and
- apply geographic data and services accessed from other organizations.
Implement an internationally standardized set of geospatial metadata information and a common set of terminology and definitions for concepts related to metadata, including:
- the names of data attributes (individual metadata elements) and classes (groups of data attributes) to be used,
- the relations among these attributes and classes,
- the definitions of these attributes and classes, and
- information about the values that can be provided for the data attributes.
Implement an internationally standardized geospatial metadata record format.
Promote an internationally standardized method for extending the standard to better address the specialized geographic data documentation needs of a specific community.
The CSDGM design model is a plain document, also known as a ‘flat file’, presented as a structured list where all sections are equal. ISO 19115 and the NAP were developed using Unified Modeling Language (UML). The UML data model provides a far more robust, object-oriented structure that helps to visualize more complex relations among the sections, the information contained in the sections, as well as information from related standards.
The NAP was developed and documented in a manner intended to interpret the ISO 19115 UML in a more practical and applicable format. UML diagrams were replaced with simplified diagrams, a data dictionary is provided, and best practices are integrated to provide insight and guidance. Current efforts are underway to further translate the NAP diagrams into the traditional format of the CSDGM graphical representation.
Using Geospatial Metadata
Digital geospatial metadata helps people who use geospatial data, or geodata, to find the data they need and determine how best to use it. Metadata supports data producers in locating and using their own geodata resources, and data consumers in locating and using geodata resources produced by others. Metadata includes compound data about the content, quality, condition, and other characteristics of geodata. The information contained in a metadata record is based on the four roles that metadata records play:
- Availability -- data needed to determine the sets of data that exist for a geographic location;
- Fitness for use -- data needed to determine if a set of data meets a specific need;
- Access -- data needed to acquire an identified set of data; and
- Transfer -- data needed to successfully process and use a set of geospatial data.
The four roles form a continuum in which a user cascades through a decision tree of choices to determine what geodata are available, to evaluate the fitness of the data for use, to access the data, and to transfer and process the data. The exact order in which particular data elements are evaluated, and the relative importance of data elements, will not be the same for all users.
The major uses of geospatial metadata are:
- To maintain an organization's internal investment in geospatial data;
- To provide information about an organization's geodata holdings to data catalogues, clearinghouses, and brokerages; and
- To provide information needed to process and interpret geodata to be received through a transfer from an external source.
With the abundance of geospatial resources available today, standardized technologies such as catalogue services are necessary to facilitate data discovery, retrieval, and maintenance.
Using standardized interface specifications, clients of different origins and with potentially different focuses can access the technology and the geospatial metadata to which each interface provides potential access. Since these interfaces are standardized, a major role in the development of catalogue services, including Catalogue Services for the Web (CSW), is left to developers, defining information models which can be used by these interfaces and yet remain independent of the underlying metadata.
Geospatial Metadata – CSDGM Application Profile
The OpenGIS® Catalogue Service Implementation Specification 2.0.1- FGDC CSDGM Application Profile for CSW 2.0 is anOGC® Best Practices document that defines an application profile for metadata documents, complying with the FGDC CSDGM specification and based on the requirements of the Catalogue Services for the Web (CSW) specification. The Profile also provides extensions to this base in several areas. The base profile provides a fundamental set of information objects that must be supported by each catalogue instance; in addition, Application Profiles for different information communities should be specified.
The Application Profile specifies the interfaces, bindings, and encodings required to publish and access digital catalogs of metadata for geospatial data that comply with the given profile. Metadata acts as generalized properties which can be queried and returned through catalogue services for resource evaluation, and in many cases invocation or retrieval of the referenced geodata information.
The Application Profile applies only to implementations of Catalogue Services for the Web (CSW) supporting the FGDC-CSDGM information model and schema. Implementations of CSW using this Application Profile are intended for purposes of publishing, inventory, discovery, and access of datasets and dataset collection resources.
Metadata in Transition
Refer to the document, Preparing for International Metadata, for a clear and concise explanation to help transition from the CSDGM to the NAP.
In broad terms, the CSGDM components can be related to NAP organizational components in the following manner:
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