Introduction
Realisation of National Spatial Data Infrastructure (NSDI) is the current national focus. NSDI is proposed as a single window mechanism for providing access to the spatial data being generated and managed by various agencies in the country. It is visualised as a network of databases consisting of the domain specific databases created and managed by various agencies like Survey of India, Geological Survey of India etc. and a central database having metadata to be managed by NSDI secretariat. Towards this, a national task force has been set up by Department of Science and technology which is looking at all the related issues including evolution of spatial database standards at various domain servers as well as the metadata standards for providing single window access to the domain databases.

This paper presents a framework for evolving the spatial data standards at the various NSDI domain servers. The framework has been proposed to a sub-group assigned with the task of defining standards under NSDI taskforce. The suggested framework addresses the following:

• Database Spatial Framework
• Database Contents along with Naming conventions
• Feature Codification for each Database element
• Database Schema defining linkages between Spatial & Non-spatial elements
• Database Quality Standards
• Strategy for implementation of the standards by Respective Domain Organisations
• Development of National Spatial Data Exchange Mechanism
• Formulation of National Spatial Data Exchange format (NSDE)
• Development of to-and-fro data converters by individual domain server for supply of data to users and for accepting data from other domain servers.

While suggesting this approach, references have been drawn from the two separate national efforts in this direction. These are

• The database design standards evolved and implemented as a part of National (Natural Resources Information System (NRIS) by Department of Space
• The Digital Vector Data format evolved for exchange of topographic data by Survey of India

Table 1. Example list of Database Contents (spatial) & naming contventions
(source : Illustrative list from NRIS Standards document)

S.N	Element	Type	Feat- Code	Attrib- table(s)
1	LUSEnnnnnn	Poly	LU-Code	LUSE.LUT	Landuse / cover map for different dates. nnnn indicates year of map preparation
2	GEOM	Poly	GU-Code	GEOM.LUT	Geomarphic units & Landforms captured from source map
3	LITHO	Poly	LITH-Code	LITHO.LUT	Rock Group/ Lithologic units
4	STRU	Line	STRU-code	STRU.LUT	Geological structures like lineament, fault, fracture etc.
5	SOIL	Poly	SOIL-Code	SOIL.LUT	Soil type, depth, texture etc., for associations / series/family etc.,
6	DRAIN	Line	DRN-Code	DRAIN.LUT	Drainage
7	CANAL	Line	CAN-Code	CANAL.LUT
8	WSHED	Poly	WS-Code	WSHED.LUT	Watershed hierarchy polygons
9	WELLS	Point	Wlcode	WELL.LUT	Location of Wells, nature of Wells, yield particulars, water quality etc.
10	SETTLE	Point	Scode	Census tables	Settlement Locations
11	ROADS	Line	Rdcode	ROAD.LUT	Road network

Spatial Framework
Almost every domain server will cover spatial database on nation-wide scale. It is therefore very important to devise a common spatial framework for all the domain servers. The components of spatial framework would be the following:

Multi-layer Registration Scheme
The requirement is for selection of scheme, which facilitates unique identification number for every tie point all across Indian Territory. The suggested approach is on the basis of Latitude/ Longitude co-ordinates. The scheme proposes selection of multi-layer registration points as the Latitude-Longitude intersections as well as permanently identifiable points like load intersection as follows:

• Lat/Long intersections up to 1 Minute interval, depending upon the level of details, as the Registration/ Tic points
• Permanent features like road intersections as additional points ; to cover map sources not having Latitude/Longitude graticule.
• Unique assignment of ID for each point all over India. There will be ten digit identification number for each registration point so as to make it unique.
  Identification scheme for points on Latitude-Longitude intersections.
  DDMMDDMMOO
  ——====**
  ——Latitude value in Degrees and Minutes
  ==== Longitude value in degrees and minutes
  **Unused - Could be used for Cadastral level points
  
  
  Identification Scheme for Permanent features
  9—==xxxxx
  9 Fixed value to save clash with Lat-Long number
  —Two digit State code (Census /NIC)
  == Two digit District code (Census/NIC)
  xxxxx Five digit Identification code for Registration point

Co-ordinate/Projection System
Adoption of Projection & co-ordinate system for each of the databases at domain servers will be another crucial aspect. While a broad consensus has to evolve at national level, as an interim measure individual servers as per the specific requirements could adopt the system of its choice. Alternatives could be Lambert conformal conic projection (LCC), Universal Transverse Mercator (UTM), Projection neutral co-ordinate system (Spherical Co-ordinate system in terms of latitude-longitudes). Initial studies indicate that for large size databases such encompassing the nation-wide coverage, it is best to adopt projection neutral co-ordinate system. However, The system adopted should be based, as far as possible, on evolution of national consensus under (NSDI) and its implementation should be transparent enough for facilitating shift to new system as and when required.