Introduction

Urbanization is the process through which cities and towns develop and grow. It includes the movement of people from rural areas to urban areas as well as movements among towns and cities (Carole Rakodi and Fiona Nunan, 2002), whereas urban footprint is the amount of land required to sustain urban metabolism, that is, to provide the raw materials on which it feeds, and process of urban waste assimilation. The basic indicator to quantify urban footprint is the proportion of built up and the reduction of other land use types. This analysis gains importance in the context of rapid urbanization and consequent pressure on land, water, energy and infrastructure. The graph of metropolitan and mega cities has continued to climb and 35 such cities now dot the Indian landscape. And scores of cities with populations in excess of 100,000 are joining the million-plus city club. India's urban issues with all their related challenges and opportunities demand the need for urban studies. India’s urban population is projected to increase to 590 million (in 2030) from 340 million (in 2008) as per the report India’s urban awakening: Building inclusive cities, sustaining economic growth. The number of Indian mega cities will double from the current three (Mumbai, Delhi and Kolkata) to six by the year 2021 (new additions will be Bangalore, Chennai and Hyderabad), when India will have the largest concentration of mega cities in the world (Chakrabati, 2001).

Urban expansion takes places in substantially different forms. In any given city, new urban expansion can take place with the same densities (persons per square kilometer) as those prevailing in existing built-up areas, with increased densities, or with reduced densities. It can take place through the redevelopment of built-up areas at higher densities, through infill of the remaining open spaces in already built-up areas, or through new development in areas previously in non-urban use. New development can either be contiguous with existing built-up areas or can “leapfrog” away from them, leaving swaths of undeveloped land that separate it from existing built-up areas. It can encroach upon wetlands, watersheds, forests, and other sensitive environments that need to be protected, as well as upon farms, fields, and orchards surrounding the city. Unplanned urbanisation is resulting in unplanned and haphazard growth of large cities with negative effects on urban dweller as well as on their environment. Thus, understanding and monitoring past and current urbanization processes is essential for sustainable urban planning. In this context, remote sensing (RS) techniques have been useful understand the spati-temporal pattern of urban areas at various scales, and as data sources for the analysis of urban land cover change (Donnay et al, 2001; Batty and Howes 2001; Herold et al, 2002).

The objective of this study is to analyse the spatio-temporal urban growth of four Indian mega cities- New Delhi, Mumbai, Kolkata and Hyderabad with a 10 km buffer around the already existing city boundaries.