![How should a map be illuminated? Not everyone saw it in the same light. Illustration by Marco Heer](https://blog.nationalmuseum.ch/app/uploads/1-300x225.jpg)
Casting light on relief map shading
In 1927, geologist Albert Heim clashed with cartographers at the Federal Office of Topography as he was convinced that their relief maps of Switzerland were depicted in the wrong light. Heim believed that the light source on maps should correspond to natural sunshine.
![Albert Heim, photographed in 1934.](https://blog.nationalmuseum.ch/app/uploads/albert-heim-portrat-233x300.jpg)
![The Siegfried Map (here sheet 473, Gemmi), which was in circulation along with the Dufour Map at the same time as Heim’s paper, also showed south-facing slopes in the shade and north-facing ones in the light.](https://blog.nationalmuseum.ch/app/uploads/siegfriedkarte-300x188.jpg)
It pains me to see the warm vineyards and villages on the sunny side of the main Valais valley on the north side of Lake Geneva and the heavily-farmed sunny slopes of the north side of the Anterior Rhine Valley in the shade, while the wooded slopes on the shady side are bathed in blazing sunlight.
![Map-Glarus-northwest-lighting](https://blog.nationalmuseum.ch/app/uploads/karte-glarus-nordwest-beleuchtung-300x188.jpg)
![Map-Glarus-southern-lighting](https://blog.nationalmuseum.ch/app/uploads/karte-glarus-sudliche-beleuchtung-300x188.jpg)
Why are most maps illuminated from the northwest?
![Not only writing from left to right, but also lighting: the mountains of the Chur Rhine Valley and the Anterior Rhine Valley are in the light on the left and in the shade on the right on the map of Switzerland produced by Aegidius Tschudi in 1560. On this map, east is on the left and south at the top.](https://blog.nationalmuseum.ch/app/uploads/tschudi-schweizerkarte-300x212.jpg)
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.