FOR all the billions of dollars worth of surveillance technology directed at North Korea as it breathes fire this weekend, its closed society is so impervious to spying that diplomats in Asia are forced to admit that they might as well rely on Google Earth.

A set of images - “North Korea Uncovered”, released by Curtis Melvin, a keen American amateur - includes a tantalising view of the site where the North Koreans detonated a nuclear device last week that diplomatic sources say may have been based on a Chinese design.

Melvin’s satellite map of the country, collated from Google Earth, reveals palaces, labour camps, mass graves and the entrance to the subterranean test base in the remote northeast of the country.

He started collecting images of the world’s most isolated country for the drier purpose of analysing the economy.

Soon he realised that the regime could seal its borders but not the skies overhead.

Other enthusiasts, including some who had served in the US military in Korea, quickly began adding data, cross-checking facts and labelling locations.

The result is a portrait of a hidden country. It is so rich in raw intelligence that even the collators may not be aware of just how many state secrets are on their website.

Railways and the electricity grid crisscross a landscape where no factories have functioned for years.

Grandiose monuments adorn empty plazas. Airfields and artillery emplacements scar the landscape. A lonely missile launching site from where the North Koreans fired off short-range missiles last week stands looking out across the Sea of Japan.

Sinister mounds mark the places where exiles believe the victims of a man-made famine in the 1990s - perhaps 1m people - were interred.

The mappers are confident that they have identified the Vinalon complex, a plant connected with hideous chemical warfare experiments.

The outlines of fences, ditches and boundaries appear to correlate with escapees’ accounts of the locations of labour camps. The mappers have also identified a public execution site.

Then there are the pleasure domes of the elite. From space they can be seen to extend like a Korean Xanadu through gardens, fountains, swimming pools and pavilions.

It is within these walls that a dynastic succession is being plotted by Kim Jong-il, the North Korean dictator, with a view to securing the political inheritance of one of his three sons.

The favourite appears to be his third son, Kim Jong-Un, 26, the younger of two boys borne to Kim by his favourite female companion, the dancer Ko Young-hee, who died of cancer in Paris in 2004.

Travellers from North Korea reported this weekend that children are being schooled in songs of praise to “our general Jong-un”.

He was educated at the international school in Berne, Switzerland, where he masqueraded as the son of an embassy chauffeur, played basketball, went skiing and made friends with the children of American diplomats.

In reality, analysts say, any “successor” will be a figurehead at the top of a collective leadership already dominated by Jang Song-thaek, the dictator’s brother-in-law and head of internal security.

For Jang’s admirers, the mappers have helpfully labelled the premises of the state security department so that anyone interested in calling in on him may do so when the right moment presents itself.

Even more useful might be the layout of the National Defence Commission compound. This body is the real power in the land. It is in his role as its chairman that Kim exercises authority, leaving to others high offices in the hollow shell that is the North Korean government.

The Korean peninsula is in a heightened state of tension this weekend as political rhetoric and military preparations have intensified in the fallout from the test last Monday.

Robert Gates, the US secretary of defence, said he saw no immediate crisis.

However, reports from Washington suggest a debate is growing within the foreign policy establishment over whether America must resist proliferation at all costs or whether it should bow to reality and negotiate with North Korea as a de facto nuclear weapons state.

The United States has been constrained in its response because two American female video journalists are due to face trial in Pyongyang this Thursday after being seized by soldiers while filming along the Tumen River that divides North Korea from China.

North Korea remains extremely sensitive to unauthorised photography.

Additional reporting: Sara Hashash

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