India will launch the world's largest census on Wednesday, with more than three million officials to take part in a vast counting exercise over the next year.
The South Asian nation, home to an estimated 1.4 billion people, faces mounting challenges in providing electricity, food and housing to its growing population.
Many of its sprawling megacities are already grappling with water shortages, air and water pollution, and overcrowded slums.
India's government calls the $1.24 billion count a "gigantic exercise of national importance" that could support "inclusive governance and evidence-based policy formulation".
The enumeration will also include the politically sensitive issue of caste, the millennia-old social hierarchy that divides Hindus by function and social standing.
The upcoming census presents a formidable logistical challenge. India's 2024 general election, the largest democratic exercise in history, was conducted in seven phases over six weeks.
The census will be carried out in two phases.
The first phase, beginning Wednesday and running until September, will involve a staggered, month-long enumeration to record details of housing and amenities.
The process will combine door-to-door visits with an option for online self-enumeration, linking to an app drawing on satellite imagery and available in 16 languages.
A second phase will focus on population data including demographic, social and economic details as well as the more contentious question of caste.
Caste remains a powerful determinant of social status in India, shaping access to resources, education and opportunity.
A caste survey conducted in 2011 was never published, with authorities citing inconsistencies in the data.
The last time comprehensive caste data was collected as part of a census was in 1931, under British colonial rule.
Governments since resisted updating the data, citing administrative complexity and concerns over potential social tensions.
For most of the country, population enumeration will take place in the weeks leading up to the reference date of March 1, 2027.
In high-altitude Himalayan regions -- including the disputed territory of Jammu and Kashmir -- it will take place ahead of October 1, 2026, before snowfall begins.
India has not conducted a census since 2011, after the 2021 round was delayed by the Covid-19 pandemic.
According to the last census, India's population was 1.21 billion.
In 2023, the United Nations estimated that India had surpassed China to become the world's most populous country, with more than 1.42 billion people.
