Jacob van Deventer's town plans
Jacob van Deventer (about 1500–1575) was a mathematician and mapmaker trained in the scholarly circle around Leuven. In 1559 King Philip II of Spain, who ruled the Low Countries, commissioned him to map the towns of the region. Over the following years he produced plans of more than two hundred of them.
He worked from angle measurements, following the method set out by Gemma Frisius in 1533 and described in our article on triangulation. The plans were drawn at a consistent scale, and they show streets, walls, canals and individual blocks.
A record of lost towns
The plans were made for the king's administration and were not printed at the time. The manuscripts were sent to Spain and are now kept in Madrid. They are valuable today because many of the towns they show were damaged or rebuilt in the wars that followed, so the plans record a street layout that could not otherwise be reconstructed.