Weeks after its chairman Eric Schmidt's secretive visit to North Korea, Google has rolled out a detailed map of the isolated state that even labels some of its remote and infamous gulags.

Until now North Korea was pretty much a blank canvas to users of Google's "Map Maker", which creates maps from data that is provided by the public and fact-checked in a similar process to that used by Wikipedia.

"For a long time, one of the largest places with limited map data has been North Korea. But today we are changing that," Jayanth Mysore, a senior product manager at Google Map Maker said in a blog posting on Monday.

Mysore said the North Korea section had been completed with the help of a "community of citizen cartographers" working over a period of several years.

"While many people around the globe are fascinated with North Korea, these maps are especially important for the citizens of South Korea who have ancestral connections or still have family living there," he added.

With the two countries still technically at war, decent maps of the North are almost impossible to come by in South Korea.

The people least able to benefit from the Google publication will be the North Koreans themselves, who live in one of the most isolated and highly censored societies on the planet.

The North has a domestic Intranet, but it is cut off from the rest of the world, allowing its very limited number of users to exchange state-approved information and little more.

Access to the full-blown Internet is for the super-elite only, meaning a few hundred people or maybe 1,000 at most, experts estimate.

The Google version offers a detailed map of the capital Pyongyang, showing hospitals, subway stops and schools.

Outside the capital, the detail is sketchier, but noticeable on an overview of the country are a series of city-sized, grey-coloured areas which, when zoomed in on, are identified as sprawling re-education camps.

In the largest gulag of all -- Camp 22 near Hoeryong near the North's northeast border with China -- Google Map Maker identifies a number of units including an armoury, a food factory and a guards' restroom.

As many as 200,000 people are estimated to be detained in the North's vast gulag system, many under a guilt-by-association system that punishes those related to someone perceived as an enemy of the state.

Google has helped cast a light on the location of these camps before, through its popular Google Earth satellite imagery service.

Groups and individuals involved with human rights research on North Korea have used the satellite pictures to confirm the location of known camps and uncover the existence of new ones.

The release of Google's new North Korea map came just weeks after Schmidt returned from a controversial trip to Pyongyang as part of a US "humanitarian" mission.

On his return, Schmidt said he had told officials in the North that the country would never develop unless it embraces Internet freedom.

Schmidt's trip was criticised by the US State Department, which said it was ill-timed in the wake of the North's recent banned rocket launch.

South Korean officials on Tuesday welcomed the Google map initiative.

"We think that this could be an opportunity for the world to know more about North Korea and an opportunity for the North to open itself more," a unification ministry spokeswoman said.

And the concept also drew praise from some of the South Koreans, cited by Mysore, with family roots in the North.

"It sounds great. I'll be happy to see the map of my hometown," said Lee Nak-Ye, who heads an association for Koreans who moved from North to South.

Lee, 80, left his home in the eastern port city of Hamhung when the 1950-53 Korean War broke out and can "only dream" of reuniting with the relatives he left behind.

"I'll tell other friends at the association about this," Lee said. "Most of them are too old to learn how to use the Internet thing though."