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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 equipments, softwares 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.
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 increaseduse 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 :-
1. Content standardization - the layers, attributes and schemas that
will populate a NSDI Node.
1.1. 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.
2. Design and Process standardization - the GIS database design
encompassing issues of co-ordinate 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.
3. Network Protocols Standards - for linking the NSDI Node servers and
their inter-server communications.
4. Exchange and Transfer Standard - file formats for the exchange of
spatial information from and to NSDI Nodes and defining output formats for
user access.
5. NSDI Quality Standards - the quality evaluation parameters and
procedures for verification and quality certification of the NSDI content.
6. In India,
we have two standards: the NRIS Standards and the SOI DVD standard. The
former is a content-based specification while the latter addresses the data
exchange issues. An attempt has been made to mergethe two to form a single
content cum transfer specification. These are the first steps in the
direction of evolving a national standard for India.
7. 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.
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