The original note, as written at the time
Developed space benefits from occupation. You do not want developed space to remain vacant for long periods of time. Unlike natural space, developed space requires maintenance and security, the latter of which sometimes just requires people to be able to traverse the place.
Ongoing development
Developed space benefits from occupation. You do not want developed space to remain vacant for long periods of time.
This sounds obvious and it is almost never designed for. We design the building and then we assume occupancy, and occupancy becomes an operational question handled by somebody else, at a desk, with a spreadsheet. But the building has a physical relationship with being used, and when it is not used, that relationship turns against it.
Unlike natural space, developed space requires maintenance and security. Natural space maintains itself — a field goes to scrub and the scrub is still a field, doing what fields do. A concrete slab does not do that. A vacant slab is a place for water to sit and for people to break in, and the two are related, because the second is what happens when the first is not noticed.
And notice how much of the security question is answered by people simply being able to traverse the place. The building with people in it during the day, walking through, using the stairs, is a building that is watched without a guard. Security, in most ordinary buildings, is not a product you buy. It is a by-product of occupation.
So the design consequence is that buildings should be made generous enough to be used lightly. If the only way to occupy a space is to fill it with paying tenants on long leases, then the space will be vacant between tenants, and vacancy is the expensive condition. If instead a building allows short occupation — partial floors, pop-ups, community use, a room let by the day, a hall that can be opened — then it stays occupied and stays cheap to keep.
This is the argument for designing mixed and loose rather than specific and tight. Every square metre that can only do one job is a square metre that is useless the moment that job ends. Every square metre that can absorb three or four uses is a square metre that is never idle for long.
And there is a social reading of the same point. A building that stays occupied becomes known, and a building that becomes known acquires a kind of informal policing that no contract provides. The reason our older streets were safe was not that they were well lit. It was that somebody was always there.