India adds another 3582 kilometres to its coastline

India's coastline has been officially recalculated to a length of 11,098.81 kilometres, a significant increase from the previously accepted 7,516.60 kilometres that had been in use since the 1970s. This revision, announced by the Survey of India (SoI), is not due to a physical change in India's landmass but rather a result of modern measurement methodologies and technologies.

The updated coastline length was determined through a comprehensive re-evaluation process involving multiple government agencies, including the Survey of India (SoI), Department of Science and Technology (DST), India and the National Hydrographic Organisation (NHO). The key changes in methodology include using the high-water line and using updated maps with higher-resolution for the measurement

The new length is measured at the High-Water Line, utilising base data from 2011 Electronic Navigation Charts (ENCs) prepared by the NHO. The recalculation also used a much larger scale of 1:250,000, compared to the 1:4,500,000 or smaller scale used for the 1970s data. This finer scale, coupled with modern GIS software, LIDAR-GPS mapping, drone imaging, and satellite altimetry, enables the capture of more intricate details, such as bays, inlets, estuaries, and minor irregularities that were previously smoothed out. The team also utilised the updated World Geodetic System 1984 (WGS84), a global geodetic datum used for determining positions on the Earth's surface. 

A significant factor in the increase is the inclusion of the peripheral coastline of 1,298 offshore islands and islets (1,059 islands and 239 islets), which were largely unaccounted for in earlier measurements due to scale constraints and manual mapping limitations.

The methodology also standardised the closing of river mouths, creeks, estuaries, and backwaters at suitable locations, considering only the segment of the length that closes the river mouth. Additionally, the length of islands connected to the mainland during low tide conditions has been added. The length of India's coastline will now be reviewed every 10 years using updated data sets.

The process of updating the coastline length has been deliberated by the Coastal Protection and Development Advisory Committee (CPDAC) since 2010. The updated Terms of Reference (ToR) were finalised at the National Security Council Secretariat (NSCS) in August 2023 and the revised length was accepted in January 2024 after concurrence from all coastal states and Union Territories.

The significant deviation from the 1970s figures is primarily attributed to the limitations of the older measurement techniques. The previous calculations relied on smaller-scale maps (1:4,500,000 or smaller) and often employed conventional or manual methods for mapping new regions. This meant that many intricate coastal features, such as small bays, islets, and the coastlines of numerous offshore islands, were either simplified or entirely omitted, leading to a shorter overall measurement. 

The updated coastline length has wide-ranging implications for various aspects of governance, like maritime security, economic zoning and blue economy planning, coastal regulation and management, environmental policy, and national security planning.

While the increase in coastline length is a result of improved measurement techniques and not a physical expansion of land, it underscores the importance of accurate geographical data for effective policy-making and sustainable management of India's vast and dynamic coastal regions.

Here is the State-wise/UT-wise length of the coastline of India: