It's New Zealand, but not as you know it.

During the Cold War, Soviet Russia secretly mapped hundreds of cities across the globe, drawing up millions of highly detailed maps of eastern Europe, Africa and Europe.

The Soviet Empire's secret mission to map the globe reached Christchurch and Wellington in 1978. The resulting maps are so detailed they could only have been made using spies on the ground in New Zealand, one expert believes.

The maps show the two cities as you have never seen them before. Familiar place names are rendered in the Russian Cyrillic alphabet, strategic buildings like police stations and airports are marked in different colours and they include some details not featured on New Zealand maps from the time.

Every fire and police station in the city is marked, along with electricity substations, court buildings, telephone exchanges, railway yards and customs buildings.

The maps also include blocks of Russian text that go into incredible detail about the landscape, infrastructure and features of the two cities.

The Christchurch map includes a detailed description of the city, including the exact gradient of the Port Hills, the depth and flow rate of the Avon, Heathcote and Waimakariri rivers, the average height of trees in the Port Hills – along with the thickness of their trunks – the exact length of the airport's main runway and detail about the capacity of Lyttelton port.

The Russians even made notes on the character of some suburbs.

"To the west of Hagley Park is located the Fendalton aristocratic district with mansions and district schools," the text states.

Central Christchurch as it appears in a 1978 Soviet Union map of the city.

One site on the Russian maps is not marked on New Zealand ones from the 1970s. A facility just west of Christchurch Airport is marked as a US military radio facility on the Russian map. Aerial photography on Google Maps shows a couple of buildings on the site behind tall wire fencing. But the facility was demolished to make way for the Pound Rd bypass in 2015, leaving only a concrete foundation.

The map describes a building on Victoria St in central Christchurch as a "nuclear research laboratory". It is in fact the former National Radiation Laboratory which operated on the site from the 1950s until 2011, conducting medical research, calibrating geiger counters and acting as the country's radiation regulatory body.

There are some errors on the Russian maps. The Press building in Cathedral Sq, Christchurch is marked as City Hall.

Central Wellington as it appears in a map made by the Soviet Union in 1978.

The detailed text on the Wellington map notes the very steep slopes of the hills around the city, the height of grass on the slopes, that the best place for off-road vehicles in the hills "are the crests of the ridges and the bottom of valleys", the rocky shoreline that "hinders navigation" and the large buildings in the city centre that "due to frequent earthquakes have strong, deep foundations".

The maps also include notes on what is made in each factory, including carpets, tyres, rubber, chemicals, glass, meat processing, wool spinning, and, in one case, "unknown rod manufacture".

A New Zealand cartographer, who did not want to be named, believed that level of detail would only have been possible with local spies.

The port town of Lyttelton in Canterbury was mapped in great detail because of its strategic importance.

"It is speculation, but I would not be surprised if they had people on the ground to check these things in New Zealand," he said.

It was likely the Russians used details from maps produced by the New Zealand Government in the 1940s, 50s and 70s.

The Russian map of Christchurch is very similar to a Kiwi one from 1947, combined with modern details from 1970s Kiwi street maps. While the Russian map of Wellington is similar to a Kiwi one from 1952.

Wellington Airport was marked as a strategic asset on the 1978 Russian map of the city.

The reason why the Soviet Empire created so many detailed maps is still a mystery. Researchers told Wired magazine that the level of detail in the maps indicated they were more than military blueprints and may have been created on the assumption that the USSR would one day have to run these cities.

Some estimate the USSR compiled millions of maps over decades, many of which were smuggled out and sold when the Soviet Union crumbled in 1989.

The 1978 map of Wellington by the Soviet Union, left, is similar to a 1952 map of the city made in New Zealand, right.