Reliable maps and instruments were essential aids for determining the course and position of ships on their voyage and often largely unknown territories. Navigation depended to a large extent on the observation of the position of the stars; no wonder that astronomy and cartography blossomed in the 17th century. This painting shows an astronomer or cartographer surrounded by his scientific instruments: globes on the cupboard and on the table, on the left a tellurium (which was used to demonstrate the movement of the earth), in the foreground, far right, an astrolabium (for astronomical and geographical measurements), next to it a quadrant and a 'Dutch Circle' (for the measurement of angles).