# Zombie Outbreak in a City

This model showcases an ABM running on a map, using OpenStreetMapSpace.

## Constructing the end of days

using Agents
using Random

We'll simulate a zombie outbreak in a city. To do so, we start with an agent which satisfies the OSMSpace conditions of having a position of type Tuple{Int,Int,Float64}. For simplicity though we shall build this with the @agent macro.

@agent Zombie OSMAgent begin
infected::Bool
speed::Float64
end

To be explicit, this macro builds the following type:

mutable struct Zombie <: AbstractAgent
id::Int
pos::Tuple{Int,Int,Float64}
infected::Bool
speed::Float64
end

where a tuple (i, j, x)::Tuple{Int,Int,Float64} means a position on the road between nodes i, j of the map, having progressed x distance along the road.

The model constructor we build consists of a map, and 100 agents scattered randomly around it. They have their own agenda and need to travel to some new destination. Unfortunately one of the population has turned and will begin infecting anyone who comes close.

function initialise(; seed = 1234)
map_path = OSM.test_map()
properties = Dict(:dt => 1 / 60)
model = ABM(
Zombie,
OpenStreetMapSpace(map_path);
properties = properties,
rng = Random.MersenneTwister(seed)
)

for id in 1:100
start = random_position(model) # At an intersection
speed = rand(model.rng) * 5.0 + 2.0 # Random speed from 2-7kmph
human = Zombie(id, start, false, speed)
OSM.plan_random_route!(human, model; limit = 50) # try 50 times to find a random route
end
# We'll add patient zero at a specific (longitude, latitude)
finish = OSM.nearest_node((9.945125635913511, 51.530876112711745), model)

speed = rand(model.rng) * 5.0 + 2.0 # Random speed from 2-7kmph
zombie = add_agent!(start, model, true, speed)
plan_route!(zombie, finish, model)
# This function call creates & adds an agent, see add_agent!
return model
end
initialise (generic function with 1 method)

In our model, zombies are seemingly oblivious to their state, since they keep going about their business, but start eating people along the way. Perhaps they can finally express their distaste for city commuting.

function agent_step!(agent, model)
# Each agent will progress along their route
# Keep track of distance left to move this step, in case the agent reaches its
# destination early
distance_left = move_along_route!(agent, model, agent.speed * model.dt)

if is_stationary(agent, model) && rand(model.rng) < 0.1
# When stationary, give the agent a 10% chance of going somewhere else
OSM.plan_random_route!(agent, model; limit = 50)
# Start on new route, moving the remaining distance
move_along_route!(agent, model, distance_left)
end

if agent.infected
# Agents will be infected if they get too close (within 10m) to a zombie.
map(i -> model[i].infected = true, nearby_ids(agent, model, 0.01))
end
return
end
agent_step! (generic function with 1 method)

## Visualising the fall of humanity

using InteractiveDynamics
using CairoMakie
ac(agent) = agent.infected ? :green : :black
as(agent) = agent.infected ? 10 : 8
model = initialise()

abmvideo("outbreak.mp4", model, agent_step!;
title = "Zombie outbreak", framerate = 15, frames = 200, as, ac)
[ Info: Created OSMGraph object with kwargs: network_type=drive, weight_type=distance, graph_type=static, precompute_dijkstra_states=false, largest_connected_component=true
┌ Warning: Since there are a lot of edges (3639 > 500), they will be drawn as straight lines even though they contain curvy edges. If you really want to plot them as bezier curves pass edge_plottype=:beziersegments explicitly. This will have much worse performance!
└ @ GraphMakie ~/.julia/packages/GraphMakie/wRCZ6/src/recipes.jl:409