How to apply texture to gameobject with texture atlas?

I'm trying to download a series of map tiles from an internet source, put them into a texture atlas, and then apply the "stitched" image as a single texture to an object. Because of the nature of the tiles, I can't simply use and use www.LoadImageIntoTexture - this will only work for a single image (I do implement this in my script, however). I read on some other forum answer that the best way to stitch images together in a collage-like fashion was to use a texture atlas. However, I've been running into issues that I believe may be due to a lack of understanding the texture atlas technique, or the C# language. I'm new to Unity.

I'm also using a coroutine within a for loop in order to populate my texture2d array. Not sure if this is the proper use of a coroutine, but I know I had to use one when experimenting with downloading a single image (waiting for the image to finish downloading in the start function) and applying it to a texture. I've been working in steps.

Each image is 256 x 256, which makes an 8x8 atlas of 2048 by 2048 pixels. I don't understand how to use the rects variable, but it was on the scripting documentation for the Texture2D.PackTextures page, so I figured I should probably include it?

Any help would be much appreciated! Here's my script for reference:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class TextureEditor : MonoBehaviour {
 
     public Texture2D[] atlasTextures;
     public Rect[] rects;
 
     // Use this for initialization
     IEnumerator Start () {
 
         int idx = 0;
         for(int i = 0; i < 8; i++) //8 cols of tiled images
         {
             for(int j = 0; j < 8; j++) //8 rows
             {
                 string URL = System.String.Format("a.maps.owm.io:8099/589a02cf24cec8000135acd1/3/{a}/{b}?hash=0135e466b47705745ffa9e6a98379755", i, j); //URL is a custom map on OpenWeatherMap.com, you may not be able to test it, but I'm not sure
                 WWW www = new WWW("http://" + URL);
                 yield return www;
                 www.LoadImageIntoTexture(atlasTextures[idx]);
                 idx++;
             }
         }
         Texture2D atlas = new Texture2D(2048, 2048);
         rects = atlas.PackTextures(atlasTextures, 0, 2048); //what do I do with this?
 
         GetComponent<Renderer>().material.mainTexture = atlas; //this was honestly a total guess of what to do. I just know atlas is a texture object, thought maybe it would work.
     }
     
     // Update is called once per frame
     void Update () {
         
     }
 }