How to: Classic population cap system - example

function OnInitID()

    -- [[ Markers ]]

    -- [[ Squad Groups ]]

    -- [[ Entity Groups ]]

    territoryPointType = {
        strategic = 1,
        fuel = 2,
        munition = 3,
        victory = 4,
    }

    _territory_point_blueprints = {
        {blueprint = BP_GetEntityBlueprint("territory_point_mp"), type = territoryPointType.strategic},
        {blueprint = BP_GetEntityBlueprint("territory_fuel_point_mp"), type = territoryPointType.fuel},
        {blueprint = BP_GetEntityBlueprint("territory_munitions_point_mp"), type = territoryPointType.munition},
        {blueprint = BP_GetEntityBlueprint("victory_point"), type = territoryPointType.victory},
    }

    TerritoryPoints = {}

    _PopCapSystemConfig = {
        default_basepop = {
            [0] = 35,
            [1] = 40,
        },
        grant_per_point = {
            -- strategic
            [1] = {
                [0] = 6,
                [1] = 7,
            },
            -- fuel
            [2] = {
                [0] = 12,
                [1] = 16,
            },
            -- muni
            [3] = {
                [0] = 12,
                [1] = 16,
            },
            -- victory
            [4] = {
                [0] = 4,
                [1] = 5,
            },
        },
    }

    for i = 1, World_GetPlayerCount() do
        local player = World_GetPlayerAt(i)
        Player_SetPopCapOverride(player, _PopCapSystemConfig.default_basepop[Player_GetRace(player)])
    end

    for index = 0, World_GetNumEntities() -1 do
        local entity = World_GetEntity(index)
        if Entity_IsOfType(entity, "strategic_node") then
            local _blueprint = Entity_GetBlueprint(entity)
            local _type

            for key, item in ipairs(_territory_point_blueprints) do
                if _blueprint == item.blueprint then
                    _type = item.type
                end
            end
            local _territory_point = {
                worldID = Entity_GetGameID(entity),
                blueprint = _blueprint,
                type = _type,
                owner = "world",
                granted = false,
            }
            table.insert(TerritoryPoints, _territory_point)
        end
    end

    Rule_Add(Monitor_TerritorySectors)
end

function Monitor_TerritorySectors()
    for key, point in ipairs(TerritoryPoints) do
        local entity = Entity_FromWorldID(point.worldID)
        local current_owner = Entity_GetPlayerOwnerSafe(entity)
        local previous_owner = point.owner

        -- Is owned by world
        if current_owner == "world" then
            if point.granted then
                --remove bonus
                if point.owner ~= "world" then
                    GrantPopulationBonus(point.owner, point.type, "-")
                    point.owner = "world"
                end
                point.granted = false
            end
        else
            -- IS owned by player
            if not World_IsInSupply(current_owner, Entity_GetPosition(entity)) then
                if point.granted then
                    --remove bonus
                    GrantPopulationBonus(point.owner, point.type, "-")
                    point.owner = current_owner
                    point.granted = false
                end
            else
                if not point.granted then
                    point.owner = current_owner
                    GrantPopulationBonus(point.owner, point.type, "+")
                    --give bonus
                    point.granted = true
                end
            end
        end
    end
end

function GrantPopulationBonus(player, _type, direction)
    local current_population = Player_GetMaxPopulation(player, CT_Personnel)
    local grant = _PopCapSystemConfig.grant_per_point[_type][Player_GetRace(player)]

    if direction == "-" then
        -- turn it negative
        grant = 0 - grant
    end

    for i = 1, World_GetPlayerCount() do
        local _player = World_GetPlayerAt(i)
        if Player_GetTeam(_player) == Player_GetTeam(player) then
            Player_SetPopCapOverride(_player, current_population + grant)
        end
    end
end

function Entity_GetPlayerOwnerSafe(entity)
    if World_OwnsEntity(entity) then
        return "world"
    else
        return Entity_GetPlayerOwner(entity)
    end
end

function Player_GetIDSafe(player)
    if not player or player == "world" then
        return "world"
    else
        return Player_GetID(player)
    end
end