Extreme density, and everyone facing the same direction — away from each other.
Four numbers decide what a crowd does: how tightly it is packed, how loud it is, how fast alcohol arrives, and how much attention is available for the people beside you. Everything below is either a published figure or derived from one.
Front of stage runs around three people per square metre — Fruin grade F, where crowd force starts to propagate through the mass rather than being absorbed by individuals. It is the densest social venue modelled here, and at 105 dB it has the second-shortest speech range: 58 centimetres.
The variable that defines it, though, is neither of those. It is orientation. Everyone in a festival crowd is facing the same way, at something deliberately designed to hold their attention, which leaves roughly a quarter of it available for the people physically touching them. The model sets attention at 0.25 here, against 0.95 in a beer tent.
The effect is visible in the output: despite the highest density of any social room, the encounter rate falls below a beer tent that is packed a third as tightly. A festival crowd is thousands of people having the same experience in parallel rather than with each other.
Measured output from a standard run: 1,200 people, 4 hours of venue time, fixed seed, no parameter overrides. Every room on this site is run under identical conditions, so these figures are a like-for-like comparison rather than a set of individually flattering runs.
The crowd is a simulation and is presented as one. What is not invented are its constants: walking speed against density, the proxemic zones, the collapse of speech range with noise, the Widmark blood-alcohol curve and the conversational group limit all come from published work, cited above and listed in full in the engine.
Every gathering below is modelled as this kind of room. Attendance figures are published numbers for the period stated.
Around 3 people per square metre, which is Fruin Level of Service F — the grade at which crowd force propagates through the mass and individuals lose the ability to move independently.
Because attention points at the stage. In this model only about a quarter of the crowd's attention is available for the people beside them, which outweighs the very high density.
Fruin's grades run from A (under 0.31 p/m², free circulation) to F (above 2.17 p/m², where crowd force propagates). Event safety planning is written against these thresholds.
Each person is one cell with a position, a body mass, a Widmark distribution ratio, an openness trait and a reserve of energy. They walk at the speed the local density allows, drink at the rate the room serves, and when two of them stay within speech range long enough, a bond forms. Most bonds are nothing.
What separates an encounter that creates something from one that does not is whether it bridges two groups that were not previously connected. A tie inside an existing group mostly restates what that group already knows; a tie across a gap carries information neither side had. That distinction is Granovetter's, and it is the mechanic the whole model turns on.
One parameter has no citation and should be read as an assumption: attention, the share of a person available to whoever is beside them rather than to a stage, a road or a rite. It is the variable that separates a street crossing from a dancefloor at similar density, and it is the one this model asserts rather than borrows.
