METRICS OF URBAN SPRAWL

Evolving appropriate measures to quantify urban sprawl is a prerequisite to develop an understanding of urban sprawl. Often, there is a lack of appropriate indicators and information concerning the cities or its status, from a holistic perspective that captures not only the economic aspects but also ecological and socio-economic aspects including livelihood of people. Given the problem of urban sprawl and its inadequate understanding to precisely determine its nature, pattern and rate of growth, there is an urgent need to characterise urban sprawl, more so from the perspective of achieving sustainable urbanisation in developing countries. Thus, a significant challenge is to identify the appropriate indicators towards achieving sustainable urbanisation.

Torrens and Alberti (2000) note that despite the level of importance given to the problem of sprawl, there remains little understanding of its determinants and its constituents, since sprawl is most often confused with sub-urbanisation. However, some researchers in the recent past have attempted to characterise urban sprawl (Barnes et al., 2001; Hurd et al., 2001; Epstein et al., 2002; Sudhira et al., 2004) using spatial metrics.

Essentially, the urban sprawl metrics aid in quantifying the process, monitoring the extent of urban sprawl and also become useful as indicators for measuring the implications of policy decisions. Although some of the indicators for achieving sustainable development have been evolved by Meadows (1998), still there isn’t any broad consensus on the appropriate indices representing all of the factors and disciplines. For managing urban sprawl in north-western European cities, Gayda et al. (2003) have evolved metrics, adopted as indicators to achieve sustainable development. Furthermore, on the lines of sustainable development framework, there also exists quantification of metrics based on the carrying capacity approach. In this case, the carrying capacity of an urban system is evaluated based on the different functions and activities of the urban systems and accordingly a certain threshold for development is set, beyond which it is detrimental to the entire system itself. The concept of carrying capacity has been in news since the seminal work by Meadows et al. (1972) on the notion of ‘Limits to growth’. In India, the NIUA (National Institute of Urban Affairs) (1996) has evolved a framework for the carrying capacity based regional planning. The essence of carrying capacity based approach on the lines of achieving sustainable development lies in the fact that a host of factors (such as assimilative and supportive capacities) are under consideration in the planning processes.

Some of the existing works on sprawl ascribe spatial extent of built-up areas derived from remote sensing data or other geospatial data as the measure of sprawl. On the spatial metrics for sprawl, entropy, patchiness and built-up density have been suggested (Yeh and Li, 2001; Sudhira et al. 2004; Torrens and Alberti 2000). In addition to this, the percentage of population residing over the built-up area to arrive at population-built-up density was considered metric for sprawl (Gayda et al., 2005; Sudhira et al., 2003). However, it still remains largely unanswered as to how and what are the appropriate metrics or indicators of urban sprawl that are sufficient to represent the process of sprawl. Although some attempts are made to capture sprawl in its spatial dimensions, still they fail to capture sprawl in other dimensions (like mobility, accessibility, resource usage, etc.) and neither do they indicate their intensity (density metrics). It is thus imperative for research to address intensity of sprawl through appropriate metrics or indicators for effective regional planning.

1.    Sprawl Indicators for Bangalore, India

From an overview of the above-discussed indicators, it is seen that amongst the most relevant sprawl indicator frameworks are that of the Costs of Sprawl (TRB) and SCATTER (EU). It is further noted that the set of indicators suggested above fit very well for countries, wherein the rates of urbanisation are almost stagnant, converse to the situations in countries, with high urbanisation rates. It is with this motivation, the current paper arrives at the indicators for sprawl on the lines of indicators developed by TRB and SCATTER, with strong relevance to the prevailing local conditions. In this regard, the suggested metrics for quantifying urban sprawl extends the city sprawl indicators of SCATTER (Gayda et al., 2005) to chiefly accommodate migration, population densities and literacy levels amongst others. The sprawl indicators are grouped under four themes:

1. Demography and Economy;
2. Environment and Resources;
3. Mobility; and
4. Planning and Governance.

1.1   Demography and Economy

The first set of indicators reflects the demographic and socio-economic characteristics of the city across different zones (core to agglomeration). The basic demographics reflect the population – native and migrant, household size, housing condition, population densities: alpha and beta density, and among the economic aspects are income levels. 

1.2   Environment and Resources

The second set of indicators capture the environmental variables and the resource consumptions that chiefly include land-use, solid waste generation and collection, water consumption and wastewater generation, and energy: consumption, sources and end-uses. The different land-uses considered are: built-up, water bodies (includes tanks and all wetlands), open land (includes barren land, rocky outcrop and dry grassland), and vegetation (includes agriculture plantations, parks, forest cover, and all green cover). For the built-up areas, some of the established sprawl metrics like, density and patchiness were computed. The solid waste management metrics consider per-capita generation and mode of collection. The water consumption per capita per day and the corresponding wastewater generated and the treatment capacities form the metrics under Water and Wastewater.

1.3   Mobility

The third set of indicators about mobility is mode of transport, modal share of public transport, mobility patterns, road traffic, average road traffic speed and travel times. The modal share of public transport, passenger-km by public modes, mobility pattern considering the average home to work travel distance and average travel time (for all modes) are part of the metrics under mobility.

1.4   Planning and Governance

The last set of indicators captures the aspect concerning planning and governance. These variables include: preparation and publication of master plans, public participation, and integration of city functions. For measuring the effectiveness of governance, the level of accessibilities to city centre, different amenities, services (including healthcare) and infrastructure are estimated. The presence/absence of elected local body and their participation in planning are also considered.