A letter for scientists at India's Maitri research station in Antarctica carrie the same PIN code as Panaji, 403001, because polar mail travels through the National Centre for Polar and Ocean Research at Vasco in Goa. 

The quirk shows how much work six numerals do for the 1.64 lakh post offices that India Post operates today, and the story of that code begins with a sorting problem more than 50 years old.

A country of similar place names

At Independence in 1947, India had 23,344 post offices, mostly in cities, but the network had to keep pace with a growing country. The Postal Index Number, introduced on 15 August, 1972, aimed to ease the sorting and delivery of mail in a land where different places often share the same or similar names and letters arrive in a wide variety of languages.

The idea came from Shriram Bhikaji Velankar, an additional secretary in the Ministry of Communications and a senior member of the Posts and Telegraphs Board. Velankar also wrote Sanskrit poetry, received the President's Award for Sanskrit in 1996, chaired the Indipex stamp exhibition in New Delhi in 1973, and retired from government service on 31 December, 1973.

What each of the six digits tells you

The length follows from the hierarchy of the code, which gives one digit to the zone, one to the sub-region, one to the sorting district, and three to the delivery post office. The first digit names one of eight regional zones, running from 1 for Delhi, Haryana, Punjab and Himachal Pradesh to 8 for Bihar........

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