Zombie population

population.ron decides how many zombies there are and where, whether emptied places fill up again, and how loud events pull the far horde toward them. Every field is optional; left out, it takes the default shown in the shipped file.

Density

density: (
    town_core: 40000.0,
    street: 32000.0,
    yard: 19000.0,
    indoors: 10000.0,
    forest_road: 7000.0,
    forest_edge: 2600.0,
    deep_forest: 650.0,
),
rooms: { "kitchen": 1.3, "living": 1.3, "bedroom": 0.8, "bathroom": 0.6 },
scale: 1.0,

Zombies per square kilometre of open ground (not walls, trees or furniture) in each zone:

Zone	Where
town_core	The civic and commercial blocks along the main street, and the street itself.
street	Roads, parking lots, sidewalks.
yard	Gardens and lots.
indoors	Any room, times the rooms multiplier for its type.
forest_road	Roads out of town.
forest_edge	Forest within forest_edge_width metres of town.
deep_forest	The rest.

scale multiplies everything (a sandbox “population” setting). core_fraction shrinks the town core along the street. On the default map this gives about 2,950 zombies. --zombies N on the command line sets the total instead and keeps the proportions.

Speed: fast_share of them (one in ten) move at fast_speed, the rest at slow_speed, in metres a second.

Respawn

respawn: (
    enabled: false,
    interval_secs: 120.0,
    min_distance: 250.0,
    seen_distance: 100.0,
    unseen_secs: 1800.0,
    top_up_below: 0.75,
    max_per_region: 6,
    max_per_check: 60,
),

Off by default. When on, every interval_secs the map’s 64 m regions are checked: one at least min_distance from every player, that nobody has been within seen_distance of for unseen_secs, holding less than top_up_below of its share, is topped back up, a few at a time. Never in or next to the house you wake up in.

Migration toward noise

migration: (
    enabled: true,
    min_radius: 25.0,
    reach_mult: 4.0,
    max_reach: 700.0,
    indoor_mult: 0.6,
    life_secs: 600.0,
    lasting_secs: 1800.0,
    spread_speed: 3.0,
    join_chance: 0.5,
    gather_radius: 12.0,
    merge_radius: 24.0,
    max_attractors: 16,
),

A sound at least min_radius metres loud (breaking a door is 26, smashing glass 22) leaves an attractor. Its pull spreads outward at spread_speed metres a second to reach_mult times the sound’s radius (at most max_reach, and indoor_mult of that from indoors), and fades over life_secs. Far zombies wandering in a region that feels the pull set off toward it a few at a time, so a big noise brings the horde in over minutes, not at once. Loud sounds close together (merge_radius) strengthen one attractor instead of making another.

Watching it

The MCP regions tool draws heat maps of living zombies and targets per region, the pull of every attractor, and the regions furthest from their targets. make_noise {x, y, radius: 120} and a few minutes of step_ticks show a horde arriving. stats gives the totals.