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Abstract
Velachery is a small ward in the Chennai Corporation area. Part of the area is facing lot of environmental problem especially during the monsoon period and creating various health hazards. The Corporation find it very difficult to implement the developmental programme, in the absence of large scale base maps, to minimise the environmental problems.The IRS-1C satellite data both PAN and LISS III data were merged. Based on the landuse information derived from the satellite merged data and using slope, soil and other attribute data, the GIS analysis were carried out to identify the problematic areas which requires immediate attention of the Corporation Engineers.The Aerial photographs on 1:6000 scale have been used for preparing large scale maps for this problematic areas for creating the data base. The TRIMBLE GPS has been extensively used for carrying out the Ground Control Survey, and in addition Levelling survey was also conducted for establishing vertical control. The Ground Controls were established using GPS and the Digital Elevation Models were measured using Planicomp Instrument at an interval of 50m. The Orthophotos were generated on 1:1500 scale using Orthocomp equipment and contour maps with a contour interval of 20cm were also prepared. The Landuse information has been interpreted from the Orthophotos. The base maps in addition to Contour maps were very useful for various developmental activities like identifying the low lying areas, flooded zones, haphazard growth of slums unauthorised contructions and the location of various service lines like Water supply line, Sewage lines etc., and the Corporation has planned a suitable measures for the Storm water drains and management from the Remote Sensing outputs. The data base created using GPS and the Aerial Photographs were found to be very effective and economical in cost, time and reliability, for implementing various developmental measures.

Introduction
Chennai is one of the important Metropolitan cities in India, the Inda's fourth largest Urban agglomeration, having more than 6.5 million population. Because of the rapid industrialisation and population growth the city has faced several problems. Since the growth of Urban population is very fast it has become extremely difficult to keep pace with growing demand for infra structural facilities including basic necessities of shelters, leading to the establishment of slums, squattors and unauthorised Constructions. The other problems that has been associated with the City growth are related to traffic and transportation, increase in land values, short supply of developed plots. The human impact on the landuse due to rapid industrialisation and urbanisation is found to be very high especially in the frings areas of Corporation limit. For proper planning and effective remedial measures the identification of problematic areas and their intensity are the concern of the Corporation Engineers. Large scale maps showing the present landuse, required for planning and development are not readily available. It would take very long time to prepare the maps by conventional methods. Aerial photographs taken during 1990 were used to generate the large scale Orthophotos on 1:1500 scale. In addition, Contours at 20m interval on 1:1500 scale were also prepared to help in planning of engineering structures required by Corporation Engineers. For Generating Orthophotos Controls were established using the Global Positioning Systems and the landuse details were updated using IRS-1C satellite data.

Objectives

1. Establishing Ground Controls by using GPS Insturment.
2. Identifying the problematic areas which requires immediate attention for the developmental work by integrating Satellite data and GIS technique.
3. Developing the data base by generating large scale Orthophotos on 1: 1500 scale with a contour interval of 20cm from the aerial photograph on 1:6000 scale.

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