“We have 1,000 favelas in Rio,” says Luna Rozenbaum. “And we intend to put all the favelas on the map.”

Rio’s sprawling shanty towns, or favelas, are home to some 15 million people.

Too unsafe, too unimportant for official cartography, was historically the government’s view. On official maps, they often don’t appear.

With half a million foreign travellers headed to Rio for the Olympics, it was time for favela residents to make their own, and put them on Google Maps.

The bustling informal settlements hold bars, restaurants, markets, kiosks, motorcycle repairmen, samba schools, hostels and a swathe of other small businesses.

Postmen don’t come here, but 85% of the residents have smartphones.

And teams of locals in each favela have been using them to map them themselves.

“We did eight favelas nearest to the Olympic Games, we started to work on them in May, and then we finished in the end of July,” says Miss Rozenbaum.

Where the streets have no name

A Rio de Janeiro native - a Cariocas - she works in a charity group called the AfroReggae Cultural Centre. She has worked there since 2011, but the centre has been around since 1993.

The houses aren’t numbered, and many streets don’t have names.

Previously, on Google Maps, these mazes of packed alleys racing up mountains with red cinder blocks appeared as vacant grey.

A “barrier of digital exclusion,” Ronan Ramos Jr, the project’s coordinator, calls this.

But the Google Street View camera, perched on a car, was never going to get up and down those hilltops.

“The people know the streets, all the people mapping live in the favelas,” says Miss Rozenbaum.

“We photograph the place, and put all the information on the smartphone, and then upload the information for Google.”

The project is called Tá No Mapa, meaning On the Map. Google has assisted with it.

As a result, 26 favelas now appear on Google Maps — including 10,000 small businesses. Since 2009, there have been hostels in the favelas, charging 20 euros a night.

A visitor to Rio staying locally brings money to the hostel owner, the motorcycle taxi driver who brings them there and back, and the restaurant next door, says Eduardo Figueiredo, who owns a hostel in a favela called Babilonia.

It is all of 750 metres from the Maracanã stadium to the bustling favela of Mangueira, known chiefly for being home to the Grêmio Recreativo Escola de Samba Mangueira, Rio’s most celebrated samba school.

About five minutes from the Olympic Stadium is Cidade de Deus, home to 400,000 residents, and subject of the 2002 film, City of God. The film’s director, Fernando Meirelles, was behind the Opening Ceremony.

President Obama visited in 2011. Brazil’s first gold medal, for judo, was won by Rafaela Silva, who grew up here in a pink home with a tin roof.

There are very poor favelas, but there are also wealthier ones located close to rich neighbourhoods, says Miss Rozenbaum.

Some are quite safe, she says. Others have local drug lords, attracting police attention and with local residents often caught - not metaphorically - in the crossfire.

A rainy night in Rio

The impact of Google Maps can already be felt.

“Everyone says that after the project, people are excited,” Miss Rozenbaum says.

“And other favelas call us to go there to do the same work, because it’s good for their businesses, their restaurants and hairdressers.”

Airbnb now has 250 listings in favelas, with two of them, Vidigal and Rocinha, cited as neighbourhoods. Both are near Leblon beach, so likely to draw tourists.

“Every business, we have in the favelas,” says Miss Rozenbaum. “Tourists go more to see the view, to drink in a bar, eat in restaurants, buy art.”

Schools and services are appearing on the map now, too.

The teams have stickers with Google Maps’ vector logo, which they give to shops as they pass, so they can show that they are now online.

The mapmakers are organised by AfroReggae, and trained by Google staff.

For the tech giant, access to the mobile phone-wielding quarter of the sprawling city’s residents who live in favelas makes sense.

And now 150 young favela residents are trained in digital marketing and mapping, points out Google Brazil’s marketing director, Susana Ayarza.

Google also worked with a bike taxi operator in Morro São Carlos, to film the first Google Street View made in a shantytown.

When the Olympics move on from Rio, it will remain a hotbed of international tourism.

A million people visited the city for Carnival last year, and the famous statue of Christ the Redeemer alone attracts 1.8 million visitors annually.

Digital maps made by hand, pointing the way to Rio’s bustling favelas, will now be able to bring needed business to small businesses like Mr Figueiredo’s hostel in Babilônia, long after the Olympics are gone.