In 1991, the dying days of the Soviet Union, a letter arrived at the BBC’s Moscow bureau addressed to me, as the service’s Moscow correspondent, with a startling request. It was from an intrepid Scottish couple who had embarked on a round-the-world trip with their three children in a horse-drawn caravan and planned to cross the Soviet Union. They wanted to know if they could rely on proper roads when traversing the sweeping stretches of steppe and desert in eastern Russia and Central Asia.

At first I was at a loss. Laying hands on a tourist plan of Moscow was almost impossible, let alone a road map of the rest of the country. And any Soviet maps that were available were littered with deliberate distortions and blanks. Along with a wider railway gauge, designed, it seems, to ensure that no European army could ever use trains to invade Russia, this was part of a long-standing policy to protect the motherland from the malevolent intent of foreigners.

Then the BBC’s driver, Vassily, chipped in. His military service had been in northern Kazakhstan. There were well-maintained military roads everywhere, he volunteered. He had travelled on some of them and seen classified Soviet maps of others. I took his word for it and passed the message on.

But only now, looking through this extraordinary book, do I appreciate the magnitude of the enterprise which back in 1991 I had gleaned just a hint of. It turns out that the Soviet government’s secret military mappers created a cartographic record not just of their own country but of the entire world, laid out in mind-boggling and unnerving detail.

Beginning in the 1940s, they charted the globe in seven different scales, capturing and storing the information in thousands upon thousands of classified maps that the rest of the world had almost no inkling of. Some laid out the topography of an area, with a focus on features that might aid or impede transport: roads, railways, bridges and mountain passes were marked, and even the density of forests and depth of rivers. Other, larger-scale maps looked at cities, providing street indexes and emphasising ‘important objects’, such as barracks and dockyards. Hundreds of symbols and colours decoded the landscapes: a thin blue line for rivers less than sixty metres wide; a thick blue line for bigger waterways; two crossed black anvils for a mine; pink shading for fire-resistant urban areas; specked green for wooded copses. As the authors of The Red Atlas, John Davies and Alexander J Kent, put it, it was ‘the most comprehensive global topographic project ever undertaken’.

On one level this is simply a book of beauty, a tale told through maps, which allows us to see our daily habitats through an exotic prism. Flipping through the two hundred-odd pages, you encounter an enthralling kaleidoscope of colour: brown and white for downtown San Francisco; bright yellow for Tokyo; swirls of blue and green for the parks and waterways of leafy Boston; bold orange for London’s twisting streets, sliced through the middle by the familiar blue snake of the River Thames.

But on another level The Red Atlas presents us with an unsettling insight into what was, let’s face it, a mammoth espionage project. Each familiar locale – and the authors give us plenty of British examples – has been rendered alien, reappropriated through Soviet eyes, meticulously translated into Russian.

Some words are hardly recognisable. Thus the London borough of Wandsworth, if we transliterate its name on the map, comes out as ‘Uondsuert’ (W is always tricky in Russian translation) and the US Air Force base of Upper Heyford becomes ‘Apper-Kheiford’.

Inevitably there are mistakes and misunderstandings. London’s Pimlico becomes ‘Timlico’. A ‘residentsia’ identified in the index as the home of ‘the Queen and the Prime Minister’ is actually Her Majesty’s Theatre near Trafalgar Square, not Buckingham Palace or Downing Street.

Some details get lost in translation. In my home town of Cambridge, one college court or quad is mistakenly labelled as a judicial court, sud in Russian. And Trumpington Road becomes ‘ulitsa Trampington-Rod’, the Russian word for street (ulitsa) perhaps added because the non-English-speaking mapmakers did not appreciate that ‘road’ (or ‘rod’) already provided the designation. Helpfully, some place names that commonly catch out foreigners are rendered phonetically. Gloucester becomes ‘Gloster’ and Leicester ‘Lester’ – useful if the maps were intended to assist an occupying Soviet force in speaking to locals as they made their way across the landscape.

And that brings us to the question that makes this project so intriguing: what the purpose of this venture was. Did Stalin really instigate this project to chart the world in anticipation of invading it? Or was it driven by ideology, in expectation of the moment when capitalism would devour itself and the entire globe would go communist? Or was the exercise more pragmatic: to codify other countries’ weak points and strategic assets on the grounds that knowledge is power, and who knows when the Kremlin might want to pinpoint NATO bases, prisons or palaces?

So how on earth did the Soviets manage to capture all this information, in such secrecy and at the height of the Cold War? The meticulous research of Davies and Kent provides some answers. To start with, it is clear that these dogged Soviet cartographers culled existing sources. One imagines them leaving Stanfords map shop in London, furtively clutching bags of Ordnance Survey maps. And open sources were supplemented by both aerial reconnaissance and on-the-spot investigation. But for Soviet embassy staff to have posed as tourists to act as map surveyors all over a foreign country would have been difficult. On both sides of the Cold War divide, diplomats’ movements were tightly controlled. So did secret Soviet agents really fan out across the globe, dispatched with notebooks, pens and tape measures, just to check the spacing between forest trees or the clearance under bridges?

This book does an admirable job of interrogating the maps to unearth the mystery of their making. But what is not yet there is testimony from retired Soviet mapmakers to fill in the gaps about how and why they went about it. Even today, it seems, Russian officials are shy of revealing too much. Perhaps – even in the era of Google Earth – this is still an active intelligence-gathering operation. We don’t yet have the full picture. Lots of room, then, for a second volume to pursue this absorbing detective story further.