Only a quarter of the total area was saved from the original topographical map of the castelline of the Brugse Vrije, which Pourbus finished in 1571. The preserved fragment represents the northeastern part of the Brugse Vrije, from Bruges to Zeeland. The identification was done on the basis of the faithful copy (0000.GRO0438.I) that Pieter Claeissens made from the damaged map in 1596-1597. The copy shows us the entire area between the Yser and Westerschelde. As the caption - partly taken from the original map - states, the different cities, villages, hamlets, inns, canals, water dikes, are depicted in separate colors. The map was the largest (23.58 m²) and one of the most accurate of the time. Due to the presence of the arms of the thirty-five crafts and of every congregation or glory, it is also interesting in the heraldic field. This fragment does not only include the most densely inhabited and most complex area of the Brugse Vrije. Moreover, it is the most accurate cartographic document of the late medieval state of the Zwin region.