Checking if a position is occupied in 2D?

Questions & Answers
1

I am wanting to only spawn something at a location IF there is nothing already there. I am new and cant work out how to do it. This is what i have so far.

Spawn Manager:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class SpawnManager : MonoBehaviour
{

    [Header("Arrays")]
    public Transform[] spawnPoints;
    public GameObject[] spawnPointsObjects;
    public GameObject temp;

    [Header("Other Variables")]
    public GameObject thing;
    int randomSpawnPoint;
    public static bool spawnAllowed;

    void Start()
    {
        spawnAllowed = true;
        InvokeRepeating("SpawnThing", 0f, 1f);
    }

    void SpawnThing()
    {
        if (spawnAllowed)
        {
            randomSpawnPoint = Random.Range(0, spawnPoints.Length);
            Instantiate(thing, spawnPoints[randomSpawnPoint].position, Quaternion.identity);
            Debug.Log("Spawned at " + spawnPoints[randomSpawnPoint]);
        }
    }
}
2

The answer to this will vary depending on exactly what you are trying to do and how exactly your game works. Looking at how you are doing it, there are 2 answers that seem plausible.
**
The general solution would just be to check if there is anything that exists in a radius around the spawn point. This is easy to do with Physics2D.OverlapCircle Unity - Scripting API: Physics2D.OverlapCircle. You can simply put all of your things on to the same layer, and then use OverlapCircle at the spawn point with that layer mask and see if it returns a hit.
**
Depending on how your game works, this solution could be fine. But lets say you have 100 spawn points, and every time you call the spawn function you always want something to be spawned somewhere. Checking random points with OverlapCircle again and again until you find an open spot can get very expensive. A more efficient way to do it would be to directly mark the spawn points as occupied. You already have a list of your spawn points, so all you need is a dictionary that will tell you if a spawn point is occupied. Dictionary<Transform, bool> spawnOccupied;. Every time you spawn something somewhere, you can just mark the spawn position as occupied spawnOccupied[spawnPoint] = true;, and then have some mechanism that will mark the spawn point as unoccupied once the enemy moves away. This will be more complicated than the first solution, but may be more efficient.