KALDARI, India — Ankaji Bhai Gangar, a 49-year-old subsistence farmer, stood in line in this remote village until, for the first time in his life, he squinted into the soft glow of a computer screen.

His name, year of birth and address were recorded. A worker guided Mr. Gangar’s rough fingers to the glowing green surface of a scanner to record his fingerprints. He peered into an iris scanner shaped like binoculars that captured the unique patterns of his eyes.

With that, Mr. Gangar would be assigned a 12-digit number, the first official proof that he exists. He can use the number, along with a thumbprint, to identify himself anywhere in the country. It will allow him to gain access to welfare benefits, open a bank account or get a cellphone far from his home village, something that is still impossible for many people in India.

“Maybe we will get some help,” Mr. Gangar said.

Across this sprawling, chaotic nation, workers are creating what will be the world’s largest biometric database, a mind-bogglingly complex collection of 1.2 billion identities. But even more radical than its size is the scale of its ambition: to reduce the inequality corroding India’s economic rise by digitally linking every one of India’s people to the country’s growth juggernaut.