This populator places the zombies in the game world.

Zombie_Populator.cs

using System.Collections;

using System.Collections.Generic;
using UnityEngine;

public class Zombie_Populator : MonoBehaviour { 
    
    //This determines how many packs of zombies will be spawned IE; how many clusters around the map, not how many zombie gameobjects
    public int PackNumber; 
    //This determines how many zombie gameobjects are in each pack of zombies
    public int PackSize; 
    //The number of zombie gameobjects in each pack can be given a random variance to give variety
    public int PackSizeVariance; 
    //When the random positions for the packs are generated, this number determines how far a zombie could be spawned from the pack center
    public float PackSizeDistance; 
    
    //This is the lower bound of the spawn area for zombies. If the spawn area is a square, this can be thought as the position of the bottom left corner 
    public Vector3 StartVector;
    //This is the lower bound of the spawn area for zombies. If the spawn area is a square, this can be thought as the position of the upper right corner 
    public Vector3 End; 
    //Because there's only one zombie gameobject, we don't need to make a list of gameobjects. We just need to make a gameobject for us to drag in our zombie prefab.
    public GameObject ZombieGameObject;
    //This is the list of the objects we have spawned already
    private List<GameObject> SpawnedGameObjects = new List<GameObject>();
    
    //We define a function that gives us a list of random positions in the spawn area defined by the upper/lower bounds. Every position represents the center of a zombie pack.
    public List<Vector3> GetSpawnVectors(){
        List<Vector3> returnList = new List<Vector3>();
        //We create a loop with the number of packs so we can generate that number of pack centers
        for (int i = 0; i < PackNumber; i++)
        {
            //We generate a random number between the x and z components of the upper/lower bounds, effectively giving us the x and z components of a random position in those bounds
            float x = Random.Range(StartVector.x, End.x);
            float z = Random.Range(StartVector.z, End.z);
            //We then use those numbers to create a new Vector3 and add it to our list which we return below
            returnList.Add(new Vector3(x, 0, z));
        }
        return (returnList);
    }
    
    //We define a function that gives us the positions of the individual zombie gameobjects in the packs. This is the function we'll be using 
    //to actually spawn our gameobjects
    //It takes in a Vector3 position and gives a list of randomly generated positions around that position
    public List<Vector3> GeneratePack(Vector3 Location){
        List<Vector3> PackSpawns = new List<Vector3>();
        //We create a loop with the number of zombies in a pack + an additional random amount between 0 and PackSizeVariance
        for (int i = 0; i < PackSize + Random.Range(0, PackSizeVariance); i++)
        {
            //We create a new Vector3 that has the x and z components of the inputed Vector3 Location modified by adding on a
            //random number between -PacksizeDistance and Packsize distance. This let the zombies spawn around the location in a circle
            //We then add  it to the list we return below
            PackSpawns.Add(new Vector3(Location.x + Random.Range(-PackSizeDistance, PackSizeDistance), 0, Location.z + Random.Range(-PackSizeDistance, PackSizeDistance)));
        }
        return (PackSpawns);
    }
    
    //This function actually places the zombie gameobjects in the gameworld. The function takes in a list of positions to generate packs around.
    public void PopulateWorld(List<Vector3> SpawnVectors){
        //We go through the list the function takes in,  calling the entry we're on x
        foreach (Vector3 x in SpawnVectors)
        {
           //We then go through the list generated by GeneratePack() when we pass in Vector3 x.
            //We are essentially going through the list above, generating the random positions around each entry,
            //And then spawning the game objects
           foreach (Vector3 y in GeneratePack(x))
            {
              GameObject z = Instantiate(ZombieGameObject, y, Quaternion.identity) as GameObject; 
              SpawnedGameObjects.Add(z);
            }
        }
    }
    
    

    

    public void DestroyAllSpawnedObjects(){
        foreach (GameObject x in SpawnedGameObjects){
            DestroyImmediate(x);
        }}


}