MUMBAI — A ttic.Caramel.Truth is not a crossword puzzle. It is the address of India's most famous monument — the Taj Mahal — on a mapping app that aims to help millions of slum dwellers, rural residents, refugees and those in need of emergency aid.

As smartphones become a common sight in developing nations and mapping technologies get more advanced, apps such as What3Words, CitoCode and Google's Plus Code are making it possible to locate even the world's most remote areas on a map.

But it is particularly useful in a country like India, where more than a quarter of the urban population lives in informal settlements which may lack street names and house numbers, said Giles Rhys Jones, chief marketing officer at What3Words.

"The lack of a formal address can be very limiting — from difficulty in receiving post to being unable to open a bank account or vote," he told the Thomson Reuters Foundation by phone from London.

"Having a uniform system is a potentially radical shift, as it enables digitization of databases of addresses, land administration geoportals, and accurate disaster and emergency service responses," he said on Friday.

What3Words divides the Earth into 3 meter x 3 meter squares and assigns each box a unique three-word address. It is available as a mobile app in 36 languages, including five Indian languages introduced earlier this year, with plans for more.

The International Committee of the Red Cross in the Philippines uses the system in disaster zones where buildings may be flattened and roads washed away.

In Mongolia, home to a large nomadic population, it is used in government documents and is recognized by many banks.

In a pilot for postal services in three Indian states last year, What3Words was faster than traditional sorting methods, Jones said, adding that it would take less than five days to provide everyone in the country a three-word address.

More than a billion people live in slums and informal settlements, according to the United Nations, and they are often denied government documentation and benefits because they lack a formal address.

"Accurate identification of a housing unit enables inhabitants to demand, access and pay for services such as electricity and water easily," said Vikram Jain, director of social consultancy FSG in Mumbai.

"Rights can be accessed when an individual can be linked to a property accurately, which allows the individual to use, transfer and inherit rights confidently," he said.

For slum dwellers in the Indian city of Kolkata, Dublin-based non-profit Addressing the Unaddressed uses GPS navigation system coordinates to create a 10-character word code that can then be located on Google maps.

"It has the potential to help a large number of people around the world," said Google spokesman Dusan Farrington, referring to Plus Code.

"Our goal is that everyone, regardless of who they are or where they live, can be found on Google maps." — Thomson Reuters Foundation