The description on the map is written in Middle-Dutch and reads:
"Gront caerte van Willems-stadt gheleghen inden ruyghen hil met haer ryvier ende hauen straten grachten boltewercken ende catten alsulcx als die in haer platte forme geleghen is. aldus gedaen deur co[m]missie vanden tresaurier van synder genaden Graeff Mauritz van Nassauwen. By myn Symon Da[m]mass van Dueren ghesworen lant-meter. Actum den 6 Janewario 1586 stilo nouo."
The translation of the description in modern English reads:
"Map of Willemstad, situated in the Ruigenhil with its river and harbour, streets, canals, strongholds and ‘katten’ (see below), as these are to be seen from above. Done as ordered by the estate agent of his merciful count Maurits of Nassau. By me, Symon Damass of Dueren, appointed as surveyor. Deed drawn up at the 6th January 1586 new style (see below)."
A ‘kat’ is part of a bastion. It is an earth wall with trees and bushes. Artillery can be placed behind it and also the wall is meant to catch canon balls.
With ‘new style’ is pointed out that the date has to be read according to the then new Gregorian calendar. Before that time, the Julian calendar was still used, but not in all provinces was the new calendar introduced at the same time.