Within the Program of Integral Knowledge of Space for Zaanstad Municipality Mathias chaired the last session before the summer break. On the 4th of July 2023 this event about the spatial problems in the soil took place underground, a more than 800m long space underneath Beatrix Bridge.

The session exchanged knowledge on the various spatial claims in the underground, such as cables, pipes, sewage, city heating and of course soil life and roots for the trees. External expert Jos van der Wersch from Leiden Municipality gave an introduction and reported of a pilot of new vertical order of installations in the soil.