**By order of General Guisan the sale of maps was banned in the Second World War.** swisstopo / Swiss National Museum

The secrets of Swiss maps

From secret maps to sales bans and retouching, various methods have been used in Swiss cartography to protect military secrets.

Felix Frey

Felix Frey is a specialist in history at the Federal Office of Topography (swisstopo).

The Swiss Armed Forces have always protected their key facilities from prying eyes. Ammunitions depots were concealed in rock faces, artillery posts disguised as chalets, armaments factories surrounded by dense forest, and military airfields shielded by barbed wire. In cartography, this secrecy led to a conflict of interests: how could topographic maps depict the Earth’s surface as realistically as possible, while not revealing any military secrets? Over the decades, the Federal Office of Topography (now: swisstopo) has repeatedly found new ways of dealing with this dilemma.

**The locations where Swiss military aircraft took off had to be kept secret from the enemy.** Swiss National Museum

A secret and an official cartography

From the late 19th century, map production in Switzerland was split into an official and a secret branch. On the one hand, the Federal Office of Topography produced the official map series, the Siegfried Map, with a scale of 1:50,000 for the Alps and 1:25,000 for the rest of the country. These maps were freely available for the public to buy. On the other, the Federal Military Department (FMD) produced a strictly confidential series of fortification maps with a scale of 1:10,000 between 1888 and 1952. As opposed to the Siegfried Map, these secret maps didn’t cover the whole country, but were limited instead to strategically important areas, such as the Gotthard region or the Rhone knee, where they were urgently needed in military fortifications as their large scale of 1:10,000 was essential for the precise calculation of artillery shooting ranges.

Detail of the Siegfried Map from 1921. — **The secret’s in the scale: Andermatt in 1921 on the Siegfried Map 1:50,000 (left) and on the much more detailed but secret Fortification Map 1:10,000 (1926).** swisstopo / swisstopo

Detail of the secret fortress map from 1926. — **The secret’s in the scale: Andermatt in 1921 on the Siegfried Map 1:50,000 (left) and on the much more detailed but secret Fortification Map 1:10,000 (1926).** swisstopo / swisstopo

The acutely dangerous situation in the First World War led the Military Department to introduce a special licence requirement to purchase the Siegfried Map, which had previously been freely available. This was intended to make it difficult for foreign spies to get their hands on up-to-date Swiss maps. While the sale restrictions were lifted in 1919, they had to be reinstated in an even more stringent form 20 years later.

Just after the outbreak of the Second World War, in September 1939, Henri Guisan, General of the Swiss Armed Forces, noted “a certain interest in Swiss map series from some quarters that warranted close monitoring.” This observation was not without cause: in May 1939, the Swiss General Staff had already suspected the German Army of specifically ordering Swiss map series via a Berlin cover address. Guisan also criticised the fact that Swiss map stocks “were not sufficient to cover extraordinary replenishment needs, not even for the delivery of a second set of new maps to authorised staff and units.” Warfare was impossible without geospatial knowledge, so in the interests of defence preparedness, every available map was therefore to be seized and handed over to the armed forces.

The Federal Council responded to the map shortage and the secrecy issue in October 1939 by completely banning the sale and export of maps of Switzerland at a scale of 1:1,000,000 or larger. The reproduction of information on Swiss terrain was also prohibited in books, newspapers and even on postcards. These measures were tantamount to widespread cartographic censorship and were only lifted after the war in the summer of 1945.

**General Guisan banned the sale of maps during the Second World War.** The Library Am Guisanplatz

Secrecy through omission during the Cold War

After the Second World War, there was a shift in the approach to sensitive geospatial data. The production of secret fortification maps was discontinued in 1952 and there were no new bans on the sale of official map series. The Siegfried Map and its successor, the National Map, which has been published since 1938, were freely and universally available in their entirety from 1945 onwards. This was not only due to peace in Europe, but also because people had realised that sales bans in other countries were largely ineffective at stopping people getting hold of certain maps.

The cartographic secrecy strategy after 1945 focused more on specifically obfuscating important military installations on maps. Military airfields, tank traps, armaments factories and many other strategically-relevant objects disappeared from maps.

Siegfried Map from 1940. — The building of the secret fortified complex near Dailly (VD), which was only vacated in 1995, still featured on the Siegfried Map of 1940. It was edited out on the first edition of the 1:25,000 map of 1962. swisstopo / swisstopo

Map from 1962. — The building of the secret fortified complex near Dailly (VD), which was only vacated in 1995, still featured on the Siegfried Map of 1940. It was edited out on the first edition of the 1:25,000 map of 1962. swisstopo / swisstopo

With or without a chalet?

By erasing sensitive objects from maps, the secrecy matter appeared to have been resolved for the time being. But discussions soon flared up about what exactly needed to be concealed and what didn’t. One group of objects caused particular concern in the 1970s: for military installations disguised as civilian buildings, for example an artillery post in the wall of a chalet, cartographic concealment achieved the opposite of what it intended. If a spy noticed a chalet on the ground that was missing on the map, it was immediately earmarked as a military object. Such installations were therefore included again on maps from 1978.

Furka without chalet. — The building of the secret fortified complex near Dailly (VD), which was only vacated in 1995, still featured on the Siegfried Map of 1940. It was edited out on the first edition of the 1:25,000 map of 1962.

And in 1978, just as one cartographic element reappeared, another disappeared. Since the terrorist threat in Switzerland had risen sharply in the 1970s, hydraulic galleries in hydropower plants were erased from maps so as not to unnecessarily facilitate acts of sabotage. The concealment of hydraulic galleries on maps continued until the turn of the millennium.

During the Cold War doubts had already been raised about the effectiveness of cartographic concealment. Ultimately, it was technological progress that brought about a change in practice as remote sensing via satellite was so sophisticated by around 1990 that concealing objects on maps made less and less sense. Continuing to hide objects would even have had the opposite effect, drawing attention precisely to the features missing on the map. From 1991, new regulations and directives were drawn up that were geared towards the so-called ‘perceptibility principle’, according to which facilities that are perceptible on the Earth’s surface should also appear on maps. This principle has proved workable and still applies today.

Space and time

This article was originally published (in German and French) on the “Space and time” website of the Federal Office of Topography (swisstopo), where readers can regularly discover thrilling chapters from the history of Swiss cartography.

More of: Modern Age 20th / 21st century Transportation War/battle Article

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