A crowd that already agrees, moving together. Shared purpose raises contact; the column keeps everyone walking.
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.
Crowd-counting methodology puts a dense marching crowd at around 2.5 people per square metre; this model uses 2.2. A march is unusual among crowds in that everyone in it has already self-selected for agreement, which is a strong prior for contact between strangers.
Working against that is the column itself. Roughly 45 percent of a march is in transit at any moment, because a march that stops is no longer a march. Attention sits at 0.55 — split between the people alongside and whatever the crowd is moving toward.
The two forces roughly cancel: 9.94 encounters per person per hour, below a carnival and well below a nightclub, but with a large connected component of 330 people. A march builds a smaller number of connections across a wider spread of the crowd — which is close to what a movement is for.
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.
By area and density. Crowd scientists estimate the occupied area and apply a density figure — around 2.5 people per square metre for a dense marching crowd, less for a loose one.
Around 470,000 participants in Washington DC, according to crowd-counting estimates by Pressman and Chenoweth.
In this model they build a wide but shallow one: fewer encounters than most venues, but a large connected component, because contact spreads across the crowd rather than concentrating in pockets.
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.
