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Proposed Frame of NSDI
The NSDI would aim to have a de-centralized approach to:
NSDI Contents
The urgent need is to encapsulate the national holdings of spatial data in digital format so that a national repository of the map information is available. The digital infrastructure would also enable greater sharing and better access to high quality spatial data and would also improve the well being of our communities. Responsible stewardship of our natural resources for sustainable development depends on making sound scientific information available to local decision makers. Quality of life in a free society is determined by the collective decisions of its individual citizens acting in the home, the workplace, and together as members of the community and these decisions requires the foundation of information, of which spatial information would be a major element. Collective decisions cannot be arrived at in a vacuum.
To start with, the rich collection of spatial data available in the country should form the foundation data for NSDI, as shown in Figure-4.1:
Figure 4.1 : NSDI Framework
Figure 4.2 : NSDI Internet
As brought out in the foregoing, there are now a large number of organizations engaged in collection and collation of data for development and planning who follow varying methods for tackling similar problems. The solutions that emerge are often confusing and at times quite contradictory. There is thus a need for standardization of an information system, which addresses major issues for sustainable development. The system should be able to handle the tasks of recording, managing designing and developing a central authority to collect and manage data and thus provide an information which is at once authoritative and reliable.
Data sets obtained from NSDI are tailored to meet the specific needs of users. It is necessary, therefore to enumerate clear-cut policies and devise strategies to implement these policies. Major constraints in developing such an infrastructure revolve around the initiative and ability of the Government to establish a platform for consideration of activities of different organizations, formulating policies and towards creation of a coordinating body. All the efforts of the Government in the field standardization will be meaningful in case it is made obligatory on private and semi Government institutions to accept and use the same. At present due to absence of efforts in the desired direction, many organizations with minimum available where withal are in the process of creating their own data standards. This can only lead to a chaotic situation.
NSDI – Design Elements
The NSDI elements, as illustrated in Figure-4.3, would be:
Figure 4.3 : Components of NSDI
The NSDI Standard
The NSDI requires a major effort at standardizing content and schemas, design and process, network protocols, exchange and transfer. The standardization has enabled “user transparency” to information access. The NSDI Standards will evolve and grow as more and more agencies commit and access the NSDI Nodes.
The definition of the spatial framework will be very crucial in the NSDI Standard and it is important that this be decided upon in the beginning. In its simplest form, it is a frame of latitudes and longitudes with intermediate tic marks aimed at providing an invariant reference for all spatial data sets. However, most users need some basic references. Thus, it also can include ortho-rectified imagery, elevation, bathymetry, geodetic control, transportation, administrative boundaries, etc. All data has to be registered to this framework so that they can be related to each other. The framework must meet the mapping accuracy desired by the applications. The choice of the geoid and the projection systems has a bearing on the accuracy. Further, the accuracy is also a function of the scale of mapping. In India, we have the advantage of having an excellent cartographic database in the Survey of India topographic sheets. These are based on the Everest spheroid and Polyconic and Lambert Conformal Conical projections. The framework of this system is ideally suited for providing the structure for a spatial database. In addition, the large-scale databases at 1:10,000 or larger scales will be on a cadastral map base – which uses using local projections. Interlinkage of these maps with the spatial framework is an involved task and no standardized procedures exist. With the increased use of Remote Sensing for thematic mapping, such inter-linkages are essential and hence this is an area in need of urgent attention.
The NSDI Standard would have to be developed and should cover:
NSDI will work with different agencies, national and international, towards establishing systematic procedures that will enable each agency to undertake standard quality audits on their spatial data. Each committing agency must declare a “Quality Certification” of their spatial data and may adopt a self-certification and quality-audit process according to the NSDI-Quality Standards. It is only after certification and audit reports are made available that the spatial data form a part of NSDI.
The NSDI Servers
The NSDI will be a set of GIS database servers – one NSDI Node for each participating agency. Thus, the NSDI will have Nodes for GSI for geological data; SOI for topographical data: NRSA for satellite images and thematic data; NRIS for natural resources management and development data; NBSSLUP for soil data and so on. Each NSDI agency will maintain its own Node as part of an Intranet and link to the “master” NSDI server.
The NSDI organization needs to ensure the following:
It is also necessary to look into aspects of Data Warehousing and related Data Mining technologies to fully utilize the enormous amount of data that is likely to be part of the NSDI. While the granularity of the data can be quite high, the data volumes would also be very high. One could use the concepts of Data Marts and Data Warehouses.
Definition of updation procedures could also be a part of the design activity so that newer data can be incorporated in future and the database is "active".
The NSDI Gateway and Intranet
Each of the NSDI Node will be on an Intranet – ensuring full security and “closed-user” access. The NSDI nodes would be linked to the master NSDI Server – which will serve as the Gateway on the Internet for the NSDI Intranet Nodes and will host the NSDI Metadata. The NSDI Master Server will also perform the role of the NSDI Electronic Clearinghouse and will “direct” access to appropriate NSDI Nodes based on access protocols.
The NSDI Gateway would be a web domain name (maybe, www.nsdi.gov.in) with individual Nodes linked to the NSDI domain.
Traffic on the NSDI is expected to be “asynchronous” with user queries of low-density and return “service” from the Nodes to the user being high-density spatial information. The NSDI Gateway on the wide area protocol and the NSDI Intranet would require sufficient bandwidth of a communication backbone. Traffic-hits on the NSDI would grow slowly and would require design of network architecture using both terrestrial and VSAT links.
NSDI Search and Access Protocols
Support of discovery and access service for spatial information in NSDI would depend upon development of a "Search service". The search engines to look for and discover data and information could adopt the Z39.90 standard (internationally adopted by spatial data infrastructures) that allows software and system independent search. Further integration of these services with web mapping, live access to spatial information, and additional services can lead to exciting user environments in which data can be discovered, evaluated, fused, and used in problem-solving. The Catalog Gateway and its user interface allow a user to query distributed collections of spatial information through their metadata descriptions. Figure-4.4 shows the possible framework for NSDI Search and Access.
Figure 4.4 : NSDI Search and Access
A user interested in locating spatial information uses a search user interface, fills out a search form, specifying queries for data with certain properties. The search request is passed to the Catalog Gateway and poses the query of one or more registered catalog servers. Each catalog server manages a collection of metadata entries. Within the metadata entries there are instructions on how to access the spatial data being described. There are a variety of user interfaces available in this type of Catalog search in various national and regional SDIs around the world. Interoperable search across international Catalogs can be achieved through use of a common descriptive vocabulary (metadata), a common search and retrieval protocol, and a registration system for servers of metadata collections.
NSDI must adopt the web browser for display and interface of queries. NSDI mapping on the Web will include the presentation of general purpose maps to display locations and geographic backdrops, as well as more sophisticated interactive and customizable mapping tools. The intention of online or Web Mapping is to portray spatial information quickly and easily for most users, requiring only map reading skills. Web mapping services can be discovered through online directories that serve both spatial data (through metadata) and services information. In fact, web mapping services are often used to assist users in spatial search systems, showing geographic context and extent of relevant data against base map reference data.
Web based mapping would provide the functionality to NSDI to help discover and visualize spatial information referenced from Catalog Servers. A Catalog Service System is implemented through Internet-based software that allows users to inventory, advertise, and access metadata and associated spatial information within a global framework of servers and also to discover data and web mapping services and then requesting and displaying maps from different servers.
Access rules will define the restrictions and categorization of users to spatial information. In addition, the access rules could also define pricing rules and ember e-commerce protocols for users to access the NSDI nodes.
Access to NSDI spatial data from the users point of view is a part of a process of that goes from discovery to evaluation, to access and finally to exploitation. Access involves the order, packaging and delivery, offline or online, of the data (coordinate and attributes according to the form of the data) specified.
NSDI Electronic Clearinghouse
Implementations of NSDI access services will be through the NSDI Electronic Clearinghouse. The clearinghouse has to have systems to authenticate data requests and requesters. Where the data is priced, the clearinghouse must provide the necessary order forms or secure transaction gateways. Spatial data volumes are usually large and download through Internet may not be feasible. In such cases, the system should be able to generate media bearing the requested data for transmission by mail. The clearinghouse should also store information about the applications and availability of application specific modules that could be reused by other users. Metadata engines which allow the user to query the data set and select records from the actual data is an area of research. Such engines are present in the background of any DBMS but they do not have the capability of distributed processing over the Web.
The sub-elements of the Clearinghouse activities would have to include the following:
Metadata helps people who use spatial data find the data they need and determine how best to use it. Metadata benefit the data-producing organization as well. As personnel change in an organization, undocumented data may lose their value. Later workers may have little understanding of the contents and uses for a digital database and may find they can't trust results generated from these data. Lack of knowledge about other organizations data can lead to duplication of effort. It may seem burdensome to add the cost of generating metadata to the cost of data collection, but in the long run the value of the data is dependent on its documentation.
It is advised not to invent one’s own standard and to build upon an internationally accepted one. The NSDI Metadata Standard; the Comité Européen de Normalisation (CEN) Pre-Standard; ISO TC 211 Standards are examples. Subtle changes from an international standard such as collapse of compound elements may be costly in the long run – making it unable to use standard metadata tools and the metadata may not be directly exchangeable or parseable by software.
There are different levels that metadata may be used for:
Each of these purposes, while complementary, requires different levels of information. As such NSDI Metadata should look at their overall needs and requirements before developing the metadata systems. The important aspect is for agencies to establish their business requirements first, the content specifications second and the technology and implementation methods third.
The major elements of Metadata includes parameters on:
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The NSDI would aim to have a de-centralized approach to:
- Develop and maintain Standard digital collections of spatial data
- Develop common solutions for discovery, access, and use of spatial data in response to the needs of diverse user groups
- Build relationships among organizations to support the continuing development of the NSDI
- Increase the awareness and understanding of the vision, concepts, and benefits of the NSDI
NSDI Contents
The urgent need is to encapsulate the national holdings of spatial data in digital format so that a national repository of the map information is available. The digital infrastructure would also enable greater sharing and better access to high quality spatial data and would also improve the well being of our communities. Responsible stewardship of our natural resources for sustainable development depends on making sound scientific information available to local decision makers. Quality of life in a free society is determined by the collective decisions of its individual citizens acting in the home, the workplace, and together as members of the community and these decisions requires the foundation of information, of which spatial information would be a major element. Collective decisions cannot be arrived at in a vacuum.
To start with, the rich collection of spatial data available in the country should form the foundation data for NSDI, as shown in Figure-4.1:
Figure 4.1 : NSDI Framework
- National coverage of topographical maps on scales of 1:250000, 1:50000 and 1:25000 and any other data of the Survey of India (SOI) toposheets
- National coverage of geological maps on 1:50000 scale and other maps/data of the Geological Survey of India (GSI)
- National coverage of soil maps on 1:250000 and 1:50000 scales and other maps/data of the National Bureau of Soil Survey and Landuse Planning (NBSSLUP)
- National coverage of forest maps on 1:50000 scale of the Forest Survey of India (FSI)
- National coverage of the hydrology maps on all scales of the Central Ground Water Board (CGWB)
- National coverage of landuse maps on 1:50000 scale; wasteland maps on 1:50000 scale; urban maps on 1:50000 scale; groundwater potential map son 1:50000 scale and other thematic maps of National Remote Sensing Agency (NRSA);
- NRIS Nodes of the NNRMS Programme involving District and State Natural Resources databases on 1:50000 scales;
- Command area maps of Central Water Commission (CWC)
- National coverage of coastal landuse maps on 1:50000 and 1:25000 scale of Ministry of Environment and Forests (MoEnF)
- Census maps and census data of the Census Department
- NATMOs national atlases on 1:1000000 and other scales
- National coverage of Satellite images of different resolutions
- Hydrographic data of the National Hydrographic Department
- To this set of basic data, addition of India Meteorological Department’s weather information and Department of Ocean Development’s Ocean information (at smaller scales) could also be added.
- Non-spatial data of the Bureau of Economics and Statistics, National Council for Applied Economic Research etc – which could be linked to the spatial features and become a part of the NSDI.
- The above is only illustrative and not exhaustive list of known agencies providing data of relevance to proposed NSDI. The NSDI would get augmented with organs of the State Governments and then in turn by non-governmental agencies – with which data may be available in various forms. Data resources of various agencies have to be studied in detail and mechanisms should be available for ensuring that this data, whenever relevant, becomes part of the NSDI.
Figure 4.2 : NSDI Internet
As brought out in the foregoing, there are now a large number of organizations engaged in collection and collation of data for development and planning who follow varying methods for tackling similar problems. The solutions that emerge are often confusing and at times quite contradictory. There is thus a need for standardization of an information system, which addresses major issues for sustainable development. The system should be able to handle the tasks of recording, managing designing and developing a central authority to collect and manage data and thus provide an information which is at once authoritative and reliable.
Data sets obtained from NSDI are tailored to meet the specific needs of users. It is necessary, therefore to enumerate clear-cut policies and devise strategies to implement these policies. Major constraints in developing such an infrastructure revolve around the initiative and ability of the Government to establish a platform for consideration of activities of different organizations, formulating policies and towards creation of a coordinating body. All the efforts of the Government in the field standardization will be meaningful in case it is made obligatory on private and semi Government institutions to accept and use the same. At present due to absence of efforts in the desired direction, many organizations with minimum available where withal are in the process of creating their own data standards. This can only lead to a chaotic situation.
NSDI – Design Elements
The NSDI elements, as illustrated in Figure-4.3, would be:
Figure 4.3 : Components of NSDI
- A NSDI Standard – defined and agreed to national agencies and defining content and schemas, design and process, network protocols, exchange and transfer. Standards are the crux of the NSDI and would be of relevance to database standardization - formats, exchange and interoperability; Networks-gateways and protocols; communication equipment, software standards, etc. Standards enable applications and technology to work together. Tools, applications, and data affect each other, and processes for developing standards must consider these interactions.
- A NSDI Metadata of the NSDI content and information availability. The NSDI Metadata would get evolved from the NSDI Standard and as digital spatial information is populated. As a part of NSDI, one of the critical steps would be the development of a metadata standard and development metadata files.
- NSDI Nodes and GIS servers of the actual spatial information – in conformity of the NSDI Standard. The NSDI Nodes would be mainly GIS based spatial databases and development oriented information systems servers - all integrated and linked to basic spatial/geographic units. The value of NSDI would be to aid as a decision-making tool and more in the context of assisting planning for developmental activities.
- NSDI Search and Access Protocols that would enable search and location of spatial information. The protocols would provide the gateway for users to access NSDI. The basic issue in the operation of the NSDI is the backbone on which the information travels from one point to another. The backbone carrier will be high-speed carrier capable of providing bandwidth on demand to intermediate levels of the NSDI and to users of the NSDI.
- NSDI Electronic Clearinghouse. The NSDI Clearinghouse would be the mechanism to provide access to the metadata and finally to the actual data sets. The clearinghouse has to have systems to authenticate data requests and requests spatial data volumes are usually large and download through networks may not be feasible. In such cases, the system should be able to generate media bearing the requested data for transmission by mail. The clearinghouse should also store information about the applications and availability of application specific modules that could be reused by other users. The clearinghouse would use the NSDI Search and access Protocols engines to look for and discover data and information.
- NSDI User Interface that would be the front-end interface for user queries and access of spatial information. With regard to design of NSDI much depends upon the level of penetration and upper-end level of applications and services available on it. For a completely ubiquitous NSDI, the penetration will have to reach public domain and the capabilities will include online access of information applications.
- NSDI Outreach and Awareness programme so as to increase the public and professional use of NSDI services and encourage e-governance concepts.
The NSDI Standard
The NSDI requires a major effort at standardizing content and schemas, design and process, network protocols, exchange and transfer. The standardization has enabled “user transparency” to information access. The NSDI Standards will evolve and grow as more and more agencies commit and access the NSDI Nodes.
The definition of the spatial framework will be very crucial in the NSDI Standard and it is important that this be decided upon in the beginning. In its simplest form, it is a frame of latitudes and longitudes with intermediate tic marks aimed at providing an invariant reference for all spatial data sets. However, most users need some basic references. Thus, it also can include ortho-rectified imagery, elevation, bathymetry, geodetic control, transportation, administrative boundaries, etc. All data has to be registered to this framework so that they can be related to each other. The framework must meet the mapping accuracy desired by the applications. The choice of the geoid and the projection systems has a bearing on the accuracy. Further, the accuracy is also a function of the scale of mapping. In India, we have the advantage of having an excellent cartographic database in the Survey of India topographic sheets. These are based on the Everest spheroid and Polyconic and Lambert Conformal Conical projections. The framework of this system is ideally suited for providing the structure for a spatial database. In addition, the large-scale databases at 1:10,000 or larger scales will be on a cadastral map base – which uses using local projections. Interlinkage of these maps with the spatial framework is an involved task and no standardized procedures exist. With the increased use of Remote Sensing for thematic mapping, such inter-linkages are essential and hence this is an area in need of urgent attention.
The NSDI Standard would have to be developed and should cover:
- Content standardization – the layers, attributes and schemas that will populate a NSDI Node.
- Each NSDI-Node agency will have to develop its own thematic content standard – GSI for geology maps; FSI for forest maps; NRSA for satellite images and thematic maps; SOI for topographical maps and so on.
- Design and Process standardization – the GIS database design encompassing issues of coordinate systems, projections, accuracies of databases, attribute schema forms etc. Further the database creation process standardization – the process and mechanics of actual database creation through manual digitization, scanning, keyboard entry of attributes and attribute file assimilation will also have to be developed.
- Network Protocols Standards – for linking the NSDI Node servers and their inter-server communications.
- Exchange and Transfer Standard – file formats for the exchange of spatial information from and to NSDI Nodes and defining output formats for user access.
- NSDI Quality Standards – the quality evaluation parameters and procedures for verification and quality certification of the NSDI content.
NSDI will work with different agencies, national and international, towards establishing systematic procedures that will enable each agency to undertake standard quality audits on their spatial data. Each committing agency must declare a “Quality Certification” of their spatial data and may adopt a self-certification and quality-audit process according to the NSDI-Quality Standards. It is only after certification and audit reports are made available that the spatial data form a part of NSDI.
The NSDI Servers
The NSDI will be a set of GIS database servers – one NSDI Node for each participating agency. Thus, the NSDI will have Nodes for GSI for geological data; SOI for topographical data: NRSA for satellite images and thematic data; NRIS for natural resources management and development data; NBSSLUP for soil data and so on. Each NSDI agency will maintain its own Node as part of an Intranet and link to the “master” NSDI server.
The NSDI organization needs to ensure the following:
- A flexibility in the design to adapt to the needs of different users.
- A system of validation checks to maintain the integrity and consistency of the data elements.
- A level of security for minimizing damage to the data.
- Minimizing redundancy in data storage.
It is also necessary to look into aspects of Data Warehousing and related Data Mining technologies to fully utilize the enormous amount of data that is likely to be part of the NSDI. While the granularity of the data can be quite high, the data volumes would also be very high. One could use the concepts of Data Marts and Data Warehouses.
Definition of updation procedures could also be a part of the design activity so that newer data can be incorporated in future and the database is "active".
The NSDI Gateway and Intranet
Each of the NSDI Node will be on an Intranet – ensuring full security and “closed-user” access. The NSDI nodes would be linked to the master NSDI Server – which will serve as the Gateway on the Internet for the NSDI Intranet Nodes and will host the NSDI Metadata. The NSDI Master Server will also perform the role of the NSDI Electronic Clearinghouse and will “direct” access to appropriate NSDI Nodes based on access protocols.
The NSDI Gateway would be a web domain name (maybe, www.nsdi.gov.in) with individual Nodes linked to the NSDI domain.
Traffic on the NSDI is expected to be “asynchronous” with user queries of low-density and return “service” from the Nodes to the user being high-density spatial information. The NSDI Gateway on the wide area protocol and the NSDI Intranet would require sufficient bandwidth of a communication backbone. Traffic-hits on the NSDI would grow slowly and would require design of network architecture using both terrestrial and VSAT links.
NSDI Search and Access Protocols
Support of discovery and access service for spatial information in NSDI would depend upon development of a "Search service". The search engines to look for and discover data and information could adopt the Z39.90 standard (internationally adopted by spatial data infrastructures) that allows software and system independent search. Further integration of these services with web mapping, live access to spatial information, and additional services can lead to exciting user environments in which data can be discovered, evaluated, fused, and used in problem-solving. The Catalog Gateway and its user interface allow a user to query distributed collections of spatial information through their metadata descriptions. Figure-4.4 shows the possible framework for NSDI Search and Access.
Figure 4.4 : NSDI Search and Access
A user interested in locating spatial information uses a search user interface, fills out a search form, specifying queries for data with certain properties. The search request is passed to the Catalog Gateway and poses the query of one or more registered catalog servers. Each catalog server manages a collection of metadata entries. Within the metadata entries there are instructions on how to access the spatial data being described. There are a variety of user interfaces available in this type of Catalog search in various national and regional SDIs around the world. Interoperable search across international Catalogs can be achieved through use of a common descriptive vocabulary (metadata), a common search and retrieval protocol, and a registration system for servers of metadata collections.
NSDI must adopt the web browser for display and interface of queries. NSDI mapping on the Web will include the presentation of general purpose maps to display locations and geographic backdrops, as well as more sophisticated interactive and customizable mapping tools. The intention of online or Web Mapping is to portray spatial information quickly and easily for most users, requiring only map reading skills. Web mapping services can be discovered through online directories that serve both spatial data (through metadata) and services information. In fact, web mapping services are often used to assist users in spatial search systems, showing geographic context and extent of relevant data against base map reference data.
Web based mapping would provide the functionality to NSDI to help discover and visualize spatial information referenced from Catalog Servers. A Catalog Service System is implemented through Internet-based software that allows users to inventory, advertise, and access metadata and associated spatial information within a global framework of servers and also to discover data and web mapping services and then requesting and displaying maps from different servers.
Access rules will define the restrictions and categorization of users to spatial information. In addition, the access rules could also define pricing rules and ember e-commerce protocols for users to access the NSDI nodes.
Access to NSDI spatial data from the users point of view is a part of a process of that goes from discovery to evaluation, to access and finally to exploitation. Access involves the order, packaging and delivery, offline or online, of the data (coordinate and attributes according to the form of the data) specified.
NSDI Electronic Clearinghouse
Implementations of NSDI access services will be through the NSDI Electronic Clearinghouse. The clearinghouse has to have systems to authenticate data requests and requesters. Where the data is priced, the clearinghouse must provide the necessary order forms or secure transaction gateways. Spatial data volumes are usually large and download through Internet may not be feasible. In such cases, the system should be able to generate media bearing the requested data for transmission by mail. The clearinghouse should also store information about the applications and availability of application specific modules that could be reused by other users. Metadata engines which allow the user to query the data set and select records from the actual data is an area of research. Such engines are present in the background of any DBMS but they do not have the capability of distributed processing over the Web.
The sub-elements of the Clearinghouse activities would have to include the following:
- Offline (e.g. packaging and physical delivery of data sets in either hardcopy or softcopy)
- Direct to datastore (e.g. soft goods delivery via ftp, specified via e-commerce order request)
- Brokered - provide specification of data access request to secondary (online or offline) access service
- Online data service (e.g. state request/response access protocol to data warehouse) supporting online operations such as - Drill down; Aggregation; Generalization
Metadata helps people who use spatial data find the data they need and determine how best to use it. Metadata benefit the data-producing organization as well. As personnel change in an organization, undocumented data may lose their value. Later workers may have little understanding of the contents and uses for a digital database and may find they can't trust results generated from these data. Lack of knowledge about other organizations data can lead to duplication of effort. It may seem burdensome to add the cost of generating metadata to the cost of data collection, but in the long run the value of the data is dependent on its documentation.
It is advised not to invent one’s own standard and to build upon an internationally accepted one. The NSDI Metadata Standard; the Comité Européen de Normalisation (CEN) Pre-Standard; ISO TC 211 Standards are examples. Subtle changes from an international standard such as collapse of compound elements may be costly in the long run – making it unable to use standard metadata tools and the metadata may not be directly exchangeable or parseable by software.
There are different levels that metadata may be used for:
- Search and Location - What data sets hold the sort of data of interest? This enables organizations to know and publicize what data holdings they have.
- Analysis metadata - Do the identified data sets contain sufficient information to enable a sensible analysis to be made for my purposes? This is documentation to be provided with the data to ensure that others use the data correctly and wisely.
- Access metadata – What is the process of obtaining and using the data that are required? This helps end users and provider organizations to effectively store, reuse, maintain and archive their data holdings.
Each of these purposes, while complementary, requires different levels of information. As such NSDI Metadata should look at their overall needs and requirements before developing the metadata systems. The important aspect is for agencies to establish their business requirements first, the content specifications second and the technology and implementation methods third.
The major elements of Metadata includes parameters on:
- Identification Information - basic information about the information set.
- Data Quality Information - an assessment of the quality of the data set.
- Spatial Data Organization Information - the mechanism used to represent spatial information in the data set.
- Spatial Reference Information - description of the reference frame for, and means of encoding, coordinates in the data set.
- Entity and Attribute Information - information about the content of the data set, including the entities types and their attributes and the domains from which attribute values may be assigned.
- Distribution Information - information about obtaining the data set.
- Metadata Reference Information - information on the currentness of the metadata information and the responsible party.