NRIS is oriented towards providing information for decision makers and encompasses information on natural resources related to land, water, forest, minerals, soil, ocean etc. and socio-economic information such as demographic data, amenities, infrastructure etc. The integration of these sets of data would aid the decision making process for systematic resource utilization Thus NRIS is visualized as a network of GIS based nodes covering the districts and states and the entire country.

The NRIS nodes are configured with huge volume of spatial and non-spatial data generated at various work centres by different set of people. Moreover, these databases have to be accessed through a set of query and decision support shells, which are user friendly and provide transparent access. As these shells are also developed by different work centres, the uniformity and validity of the databases against laid down NRIS standards is of uproots importance.

For maintaining the uniformity NRIS standards have been laid out which spells out node database contents along with associated coding scheme for each element and structure of database organization including the spatial framework and schemes for linking spatial and non spatial elements in the database.

Furthermore an approach and S/W module has also been developed and implemented for maintaining the integrity of database contents vis – a vis feature codification scheme referring to master templates.

Software Requirements
Currently NRIS databases are created using UNIX based ARC/INFO GIS software. So this module has been developed using ARC Macro Language (AML).

Methodology
The module refers to a pre-created checklist of all the database elements, which should exist in a typical NRIS node. The checklist contains

• the name of spatial layers (as per NRIS convention)
• type of spatial feature (poly, line, point)
• the name of attribute table containing the attribute descriptors for spatial features
• The name of the key field which links the spatial layer and attribute table.
• Database definition of the key field as per NRIS standard
• Range of values of key field, allowed , as per NRIS standards
• List of columns in attribute table which contain the description for spatial features (designated as per NRIS standards)

The validation module loops through this checklist and performs detailed validation checks as described below.

The first step in validation is the check on existence of the data elements. After ascertaining the existence of spatial and attribute components of the desired data element, the module proceeds further for verifying the correctness of data element from three considerations viz. a) spatial fidelity of the data element as a correct GIS layer. b) Spatial fidelity of the layer against laid down spatial framework under NRIS. c) Correctness of the feature codification as against laid down NRIS standards

Checking the spatial fidelity against GIS conventions
Module checks for the correctness of topology of spatial data elements. Depending upon the type of feature specified in checklist, i.e. polygon, line, point, the checks are performed on whether,

• layer is free of label errors
• whether requisite topology exists or not

Spatial fidelity against laid down spatial framework under NRIS.
Under this section, checks are made on projection/co-ordinate system used; adoption of scheme for identifications of registration points, spatial extend of the data elements and whether the tolerances are as per specified standards. Correctness of feature codification against NRIS standards
Checks are made for

• Existence of key field in spatial layer.
• definition of key field against specified standards
• range check for key field values against standards
• existence of feature attribute table as per naming convention
• existence, definition and value ranges of the key field
• existence of additional descriptive columns in the attribute table

At the end of checking, the errors are classified into critical errors and warning and these are logged into an error report. If a data layer shows any critical error, it is flagged as NOT OK. An error report is generated in form of a summary and detailed. The summary indicates against each element, the status as OK, NOT OK or ABSENT. The detailed report describes the types of error detected, which can be referred for carrying out corrective actions. The validation report is compared with the mandatory requirements of each of the query and decision support shells and filter condition is set for accessibility of the data case through each shell

Second part of the module is little more proactive in the sense that it corrects certain inconsistency in the database vis-à-vis master templates defined as standards. This part facilitates the following:

1. Downloading the feature attribute tables, from already created master templates as per NRIS standards, in cases where these do not exist in the database.
2. In cases where feature attribute tables are available in the databases, it corrects the human entry errors using master templates vis-a-vis the following:
   • Blank columns left in the tables are filled with the correct descriptions referring the master template via standard key codes.
   • Spelling mistakes in the descriptive fields of the attribute tables are corrected using the contents from master templates.

Results and Conclusion
The modules developed for validating and maintaining the integrity of NRIS databases has been implemented on 30 NRIS node locations at 17 state Remote Sensing Applications Centre (SRSAC) all over country. These are being operationally used by SRSAC personnel for carrying out quality assurance checks on the databases created by a set of private entrepreneurs. The task of digital quality check on NRIS databases, which is very time consuming and requires very sophisticated skills, have been turned into press of a button away. This has also facilitated a level of uniformity amongst various databases created and organized by a set of organizations (including state govt. agencies and private entrepreneurs) spread all over country. Further more, the uniformity of databases have lead to hasslefree access by a set of Query and Decision Support Shells, again designed and developed by a set of S/W experts spread all over country.

References
National (Natural) Resources Information System: Node design and standards (SAC/SIIPA/NRIS-SIP/SD-02/98), Space Applications Centre.

Acknowledgement
The authors are thankful to Shri A.R.Dasgupta Dy. Director, SIIPA for guidance and encouragement. Special thanks are due to various colleagues from SIIPA, specifically SHRI I.C.Matieda, Shri Akash Shah for providing systems support.


Flow of Validation Module