Street crossing vs Nightclub
If density made people meet, Shibuya would be the most social place on Earth.
Side by side
Conditions are published figures or derived from them. Output is measured from a standard run — 1,200 people, 4 hours, fixed seed, identical for both rooms. A highlighted cell is only marked where “more” is actually better; density and volume are conditions, not scores.
What the difference actually is
On the two variables a nightclub optimises, a scramble crossing already wins. It runs at 3.5 people per square metre against a dancefloor's 2.0, and at 75 dB against 100 — so speech carries 2.77 metres instead of 75 centimetres. More people, closer together, in a room where you can hear them.
It produces 0.20 encounters per person per hour. The nightclub produces 17.63. Over four hours, 1,200 people at the crossing leave nine lasting ties between them and the largest connected group in the entire crowd is seven people.
The variable neither density nor sound level captures is whether anybody is available. Everyone on a crossing has a destination and about forty-five seconds to reach it. In the model that is a transit factor of 0.01 — a person moving with purpose is a hundredth as reachable as a person standing still. It is the single largest effect in the whole system, and it is invisible in every photograph of a crowd.