Over the past 30 years, Kolkata has added 8 sq km of built-up area every year and according to recent research, the Metro is no exception to the global urbanisation trends. Although Kolkata lost the top spot as the most populous city in the country during 1981 Census, and even slipped to third spot during the recent Census (2011), the city, however, continues to grow in size; i. E., spatially. A paper published in Applied Geomatics by researchers from the Indian Institute of Science (IISc), Bangalore has used satellite remote sensing datasets, including NASA's Landsat mission and Survey of India's topo-sheet to ascertain the extent of growth. According to the land-use analysis, the extent of built-up area in 1980 was 72.66 km2 (about 2per cent), which has increased to 314.3 km2 (8.6 per cent) during 2010. Thus, on an average, about 8 sq km of built-up area has been added every year, according to a Gubbi Labs release. The study has also estimated several other landscape metrics used to quantify urban sprawl.
Among them, the Normalised Difference Vegetation Index (NDVI), a measure to analyse vegetation reveals a marked decline in the area under vegetation: from 36 per cent (in 1980) to 13 per cent (during 2010). Shannon's entropy, a popular measure of urban sprawl, has steadily increased particularly in the last decade (2000-2010) and more dominantly in the south-west direction. The landscape metrics computed for the built-up areas indicate that the outskirts of the city is highly fragmented and underscores the need for planning to address this. The study notes that the city's centre has been reduced to a single urban patch without any other dominating land uses during 2010. Fragmented growth in peri-urban areas has increased in 2010. It points out that lack of ecological appreciation of urban landscapes can be disastrous and hence it is important for land-use planning to factor these too. It recommends an interdisciplinary study to understand the complex interactions of the urban system so as to aid in better planning.