This mechanism is based loosely around the notion of sustainability. Spaces which receive direct light at least once per day will provide pleasanter surroundings than others and give rise to a mix of activities. The algorithm used here resembles the one used in the mass distribution, but contains some idiosyncrasies. Agents move around the site checking to see if it can see the sun from its position. If in cannot see the sun then the agent will cause the closest building between itself and the sun and reduces the height of this building unit, so the agent can now see the sun.