Map India 2000 - Poster :GIS applications for Urban Planning - A case study of Tinidivanam Town, Tamil Nadu

GIS Data Base Design for Tindivanam Town
The primary task of GIS data base for Tindivanam Town is to identify the geographic base to which all the geographical data base be attached. The smallest scale of all the theme was Master Plan on 1: 7920 scale. The largest scale was the line map from aerial photo of 1:2500 scale. The user department requirement is that all the base need to be referred to Master Plan for analysis and decision making. As conversion of large to small scale have better accuracy and so the user department's requirement of comparing all the themes to Mater Plan base. It is also noted that no theme is geo-referenced and in different scale. As a first task, it was decided, to geo-reference at least one theme and convert it to 1: 7920 scale which would allow to overlay Master Plan on it. The routine practice of geo-referencing tics, it was realized, would not help to orient the base exactly, the topo-sheet of 1: 25000 was scanned and enlarged to 1: 2500. Keeping this at the background, the digital line drawing was oriented to the topo base using AutoCAD. As AutoCAD allows objects to rotate, move, scaled, the line drawing could be adjusted comparing all the features such as road, railways, build-up areas and tanks. From this, the geo-referenced tics were prepared using the latitude and longitude of the topo sheet.

All other themes like Master Plan, DDP, water supply network, location of social features were transformed using AutoCAD to the common geo-referenced tics. Later, all the themes were exported to PC ARC/INFO for building topology and adding attribute data to all polygons of each theme. To handle better out put quality, each of the theme was plotted to master Plan scale.

User department feedback
Theme wise GIS data base were submitted to the user department in one hard copy and in CD. When the feed back was collected, the user department felt that the data base do allow analysis and query across the theme but with limited positional accuracy between themes. Positional accuracy of line map was better with DDP that with the Master Plan. It is surprised to note that the positional accuracy between Master Plan and DDP was relatively poor. It had happened due to the following reasons:

The source map for each theme was drawn from various scaled maps with different accuracy
Age of the geographic features in each theme various
Type and method of projection adopted by each source theme were different
Method of original composition of each theme's geographic feature were different

Enhancement of GIS data base It is critical to review the utility of the GIS data base generated of TIndivanam Town. Comparing to the original user department's need the out put was not fully met by the GIS data base. It is also clear that the errors introduced by the base of each theme were the cause for inaccuracies. it goes back to the vicious cycle of first developing accurate base map and then develop GIS on it. Each departmental spatial resolution and dating of spatial and attribute data swings between each property (eg. water supply) and to wards (eg. ward committee) and to town level (land use analysis). It is time to constitute a statutory body to look into these needs of each department and lay down norms and standards for spatial data base. This has to be viewed in the availability of high resolution satellite imagery accessible to user organizations at moderate cost and closer time interval (spaceimaging.com). It may lead to catastrophe of worst than paper map each development handle at present which are at least visible, being hard copy, for comparison even at different scale.

Acknowledgement The author wish to thank the Commissioner of Town and Country Planning, Government of Tamil Nadu for sponsoring the project of GIS data base for Tindivanam Town, which form the basis for this article. However, the expressions made by author is of his own and not represent the development's view.

References
DTCP (199 ) Master Plan for Tindivanam Local Planning Area, Directorate of Town and Country Planning Department, Government of Tamil Nadu. Sekar S.P. (1997) " Development Control as a source of Planning Information : a GIS model for Chennai Metropolitan Development Authority" Unpublished Ph.D. Thesis, School of Architecture and Planning, Anna University, Chennai.