1. INTRODUCTION

The study of urbanisation has evinced interest from a wide range of experts. The multidisciplinary gamut of the subject invokes the interest from ecologists, to urban planners and civil engineers, to sociologists, to administrators and policy makers, and finally the common man. This is because of the multitude of activities and processes that take place in the urban ecosystems everyday. Urban ecosystems are the consequence of the intrinsic nature of humans as social beings to live together. Thus when the early humans evolved they settled on the banks of the rivers that dawned the advent of civilisations. An inadvertent increase in the population complimented with creativity, humans were able to invent wheel and light fire, created settlements and started lived in forests too. Gradually, with the development of their communication skills by the form of languages through speech and script, the humans effectively utilised this to make enormous progress in their life styles. All this eventually led to the initial human settlements into villages, towns and then into cities. In the process humans now live in complex ecosystems called urban ecosystems.

An unprecedented population growth and migration, an increased urban population and urbanisation are inadvertent. More and more towns and cities bloomed with a change in the land use along the myriad of landscapes and ecosystems found on earth. Today, humans can boast of living under a wide range of climatic and environmental conditions. This has further led to humans contributing the urban centres at almost every corner of the earth. These urban ecosystems are a consequence of urbanisation through rapid industrial centres and blooming up of residential colonies, also became hub of economic, social, cultural, and political activities.

To understand the various components and processes that play an important role in the ecosystems are necessary to be understood. This requires a holistic approach dealing with the various components of the ecosystem. Looking back from the formation of the earth, the origin of life and subsequent evolution of life adds more light into the understanding of the current significance of urban ecosystems. The role of scientific and technological innovations in driving the urban ecosystems is an important aspect that is to be considered in the prevalent conditions. The changing lifestyles coupled with rapid urbanisation has also implicated on the material and energy cycles that have a participation in the urban ecosystems apart from the living organisms. Ultimately a clear-cut understanding of the urban ecosystem will enable us to appreciate various life processes and phenomena-taking place. The paradox of the human civilisation today is the inability to appreciate the enormous amounts of biotic and abiotic interactions that play a role in the survival and normal operation of the various ecosystem functions.

In the recent years "sustainable development" is a commonly used terminology among various sections of the society subsequent to the publication of Brundtland report in 1987. The Rio 1992, Agenda 21, all endorsed this need. The sustainable development is defined as, "development that meets the needs of the present without compromising the ability of the future generations to meet their own needs" (World Commission on Environment and Development, 1987). In order to sustain development, the supply and quality of major consumables and inputs to our daily lives and economic production - such as air, water, energy, food, raw materials, land, and the natural environment needs to be taken care of. Land is essential because our food and raw materials originate from them and is a habitat for flora and fauna. Similar to other resources it is a scarce commodity. Any disturbance to this resource by way of change in land use e.g. conversion of forestland, agricultural land into built-up, is irreversible. The use of land unsuitable for development may be unsustainable for the natural environment as well as to the humans. 

In India, with an unprecedented population growth and migration, an increased urban population and urbanisation is inadvertent. More and more towns and cities are blooming with a change in the land use along the highways and in the immediate vicinity of the city. This dispersed development outside of compact urban and village centres along highways and in rural countryside is defined as sprawl (Theobald, 2001). Urbanisation is a form of metropolitan growth that is a response to often bewildering sets of economic, social, and political forces and to the physical geography of an area. Some of the causes of the sprawl include - population growth, economy, patterns of infrastructure initiatives like the construction of roads and the provision of infrastructure using public money encouraging development. The direct implication of such urban sprawl is the change in land use and land cover of the region.

Sprawl generally infers to some type of development with impacts such as loss of agricultural land, open space, and ecologically sensitive habitats. Also, sometimes sprawl is equated with growth of town or city (radial spread). In simpler words, as population increases in an area or a city, the boundary of the city expands to accommodate the growth; this expansion is considered as sprawl. Usually sprawls take place on the urban fringe, at the edge of an urban area or along the highways.  

In industrialised countries the future growth of urban populations will be comparatively modest since their population growth rates are low and over 80% of their population already live in urban areas. Conversely, developing countries are in the middle of the transition process, when growth rates are highest. The exceptional growth of many urban agglomerations in many developing countries is the result of a threefold structural change process: the transition away from agricultural employment, high overall population growth, and increasing urbanisation rates (Grubler, 1994). The biggest challenge for science, engineering and technology in the 21st century is how to ensure adequate housing, sanitation and health, and transportation services in a habitable urban environment in developing countries. Sprawl is seen as one of the potential threats for such development.

Normally, when rural pockets are connected to a city by a road, in the initial stages, development in the form of service centres such as shops, cafeteria, etc. is seen on the roadside, which eventually become the hub of economic activities leading to sprawl.  Eventually a significant amount of upsurge could be observed along these roads. This type of upsurge caused by a road network between urban / semi-urban / rural centres is very much prevalent and persistent in most places in India. These regions are devoid of any infrastructure, since planners are unable to visualise this type of growth patterns. This growth is normally left out in all government surveys (even in national population census), as this cannot be grouped under either urban or rural centre.  The investigation of patterns of this kind of growth is very crucial from regional planning point of view to provide basic amenities in these regions. Further, with the Prime Minister of India's pet project, "Golden Quadrilateral of National Highways Development Project" initiative of linking villages, towns and cities and building 4-lane roads, this investigation gains importance and significance. Prior visualising of the trends and patterns of growth enable the planning machineries to plan for appropriate basic infrastructure facilities (water, electricity, sanitation, etc.). The study of this kind reveals the type, extent and nature of sprawl taking place in a region and the drivers responsible for the growth. This would help developers and town planners to project growth patterns and facilitate various infrastructure facilities. In this direction, an attempt is made to identify the sprawl pattern, quantify sprawl across roads in terms of Shannon's entropy, and estimate the rate of change in built-up area over a period with the help of spatial and statistical data of nearly three decades using GIS. 

The process of urbanisation is fairly contributed by population growth, migration and infrastructure initiatives resulting in the growth of villages into towns, towns into cities and cities into metros. However, in such a phenomenon for ecologically feasible development, planning requires an understanding of the growth dynamics. Nevertheless, in most cases there are lot of inadequacies to ascertain the nature of uncontrolled progression of urban sprawls. Sprawl is considered to be an unplanned outgrowth of urban centres along the periphery of the cities, along highways, along the road connecting a city, etc. Due to lack of prior planning these outgrowths are devoid of basic amenities like water, electricity, sanitation, etc. Provision of certain infrastructure facilities like new roads and highways, fuel such sprawls that ultimately result in inefficient and drastic change in land use affecting the ecosystem. With respect to the role of technology in urbanisation, Berry (1990) has illustrated a new linkage between transport infrastructure development cycles and spurts in urbanisation.   

Urban infrastructure development is unlikely to keep pace with urban population growth. Both local environmental impacts, such as deterioration of water quality in streams and an increased potential for harbouring disease vectors, and offsite land cover changes, such as the loss of woodland and forest to meet urban fuel wood demands, are likely to occur (Douglas, 1994).  

Mapping urban sprawl provides a "picture" of where this type of growth is occurring, and helps to identify the environmental and natural resources threatened by such sprawls, and suggests the likely future directions and patterns of sprawling growth. Analysing the sprawl over a period of time will help in understanding the nature and growth of this phenomenon. Ultimately the power to manage a sprawl resides with local municipal governments that vary considerably in terms of will and ability to address sprawl issues.  

GIS and remote sensing are very useful in the formulation and implementation of the spatial and temporal changes, which are essential components of regional planning to ensure the sustainable development. The different stages in the formulation and implementation of a regional development strategy can be generalised as determination of objectives, resource inventory, analysis of the existing situation, modelling and projection, development of planning options, selection of planning options, plan implementation, and plan evaluation, monitoring and feedback (Yeh and Xia, 1996). GIS and remote sensing techniques are quite developed and operational to implement such a proposed strategy. The spatial patterns of urban sprawl on temporal scale is studied and analysed using the satellite imageries and cadastral data from Survey of India, mapped, monitored and accurately assessed from satellite data along with conventional ground data. The image processing techniques are also quite effective in identifying the urban growth pattern from the spatial and temporal data captured by the remote sensing techniques. These help in delineating the growth patterns of urban sprawl such as, the linear growth and radial growth patterns. 

Mathematical models and computational techniques merely increase the capabilities of generating information that can be used in the decision making process. A model is a simplified representation of the physical system. Some simplified definitions of models are - a representative of the system that attempts to reproduce its significant elements of the system. A model is simply the symbolic mathematical form in which a physical principle is expressed.  Models are basically built by consideration of the pertinent physical principles operated on by logic and modified by experimental judgment and plain intuition. 

It is important to recognise that modeling is a part of science and part of art. The science part involves identifying the physical principles that affect the system. The artistic part consists of deciding which of these processes are sufficiently important with respect to the goals and objectives of the study to be included in the model and placing the processes in a form that reflects the interaction involved. The artistic part also involves simplification of the system so that model solutions can be achieved with a reasonable effort but without a loss of rationality or accuracy. 

Models synthesise and act as the "glue" between the perception and problem, the observational data from the laboratory and field, and the current state of scientific understanding. However, it should always be stressed that modellers and their models do not make management and control decisions but only provide information to the process. 

The model should and can reflect the dynamic characteristic and evolutionary nature of the environment. Its most important function is to establish a basis for a comprehensive plan of the entire area. Given a set of criteria, the model would analyse the alternate engineering solutions to achieve this level. Given the necessary social inputs and constraints, it would be possible to arrive at optimal solutions between the limits of some acceptable minimal treatment and maximum technologically practicable treatment. The main objectives of models are:

Environmental modelling as one of the scientific tools for prediction and assessment is well established in the field of environmental research (Ferda K, 1993). Environmental modelling has a considerable history and development. The analytical approaches applied to biological and ecological problems date back to Lotka-Volterra and the fields like hydrology - water quality modelling also date back to early twentieth century with Streeter-Phelps. With the enhanced computational techniques using microcomputers, the numerical solutions to these have become feasible. There are a variety of models in environmental studies, which will suit specific situations. For urban growth modelling suitable models can be used as effective tools in management of urban growth and population growth leading to land pressures. Depending on the type of method employed in the construction of equations, the models can be classified into four types –  

  i.              Analytical Models - These are the models, which involve construction of solutions of partial differential equations, which represent the urban systems and the land use changes considered spatially.

ii.              Numerical Models - These are the models in which an attempt has been made to represent the natural systems and to solve the equations, which describe the conventional, numerical methods.

iii.              Physical Models - These models involve construction of physical system at a smaller scale. These types of models are least employed because of the lack of knowledge of scaling relationships, and thus limitations experienced in simulating urban growth processes

iv.              Cartographic Models - A cartographic model is a graphical representation of the data and analytical procedures followed methodically in a specific study. The purpose of a cartographic model is to help the analyst organise and structure the necessary procedures as well as identify all the data required for the analysis.

There are two basic reasons for constructing representations of urban systems through mathematical modeling. First is the need to increase the level of understanding of the cause-effect relationships operative in urban growth dynamics, and secondly, to apply that increased understanding to aid the decision making process for the urban growth management.

GIS serves theoreticians, programmers, and practitioners alike. An understanding of GIS modeling is important for practitioners who will create the models; theoreticians, who develop the concepts of new models; and programmers, who must code to make the models work inside a GIS. The GIS automates geographic concepts, assists in decision-making, helps explain distributions and can assist in hypothesis formulation and testing. These tasks can be applied to a wide range of both practitioners and theoreticians by allowing them to manipulate portions of the earth that are stored as map data in the computer. The current popularity of GIS is in the multitude of domains in which they can be applied and in their ability to automate simple but repetitive map based tasks as well as complex ones (DeMers, 2002). Especially these tools enable the user to collate, integrate, analyse and model a large amount of spatial data along with their attribute information. Harnessing the total potential of the GIS in environmental modeling rests with the user capable of understanding the concepts of environmental systems and applications of GIS. 

The real world cannot solely be represented in two dimensions as is commonly accepted. This certainly is a very limiting view of the reality that we perceive around us. Most modelling in GIS has been two dimensional especially in the context of urban planning. The development in the field of "fuzzy logic" and "artificial neural networks" is providing the option of incorporating indeterminate and ambiguous information from the real world into GIS. This will be particularly useful while considering the cognitive models and individual perception of people and incorporating them for reference into GIS (Agarwal, P., 2000). 

The main objectives of this study are

 These objectives are attained through the following approach: