Looping through my JSON to spawn objects

Well, first of all Unity's JsonUtility class only accepts an object as top most element. You have an array as top most element. So one solution is to wrap your original json in a wrapper object and parse that result.

Next problem could be your nested array. Though as far as i remember it was able to deserialized jagged arrays which the normal Unity serializer doesn't support. So using proper classes to represent your data and wrapping your json in an object should work with the JsonUtility.

[System.Serializable] public class Wrapper { public YourObjectType[] data; }

 public static YourObjectType[] ParseObjects(string json)
 {
     json = "{ \"data\":" + json + "}";
     Wrapper wrapper = JsonUtility.FromJSON<Wrapper>(json);
     return wrapper.data;
 }

Of course "YourObjectType" would be also a serializable class that represents one of your objects and would look something like this:

 [System.Serializable]
 public class YourObjectType
 {
     public double[][] coordinates;
     public int type;
     public TagObject tags;
 }
 
 [System.Serializable]
 public class TagObject
 {
     public string c;
     public string t;
     public string s;
     public double h;
     public double l;
 }

Note that your "tags" object of course can't be "variable". object serialization has to be exact.

However if you want a more dynamic approach you would need to use a generic parser that doesn't serialize the data to fix classes but rather just parses the data into simple structures where you can access your data.

In your code above you use "JSONObject", however it's not clear where that class comes from. I suspect you use this JSONObject? While this framework does certainly work, personally i never used it for several reasons. The parsing is quite inefficient as it calls it's Parse method recursively and copying / duplicating alot of the input string. This is not really a problem for small json files but can become a problem if you have large files / large fields. Also ever JSONObject instance contains fields for all kind of data which makes it quite large. It also doesn't seem to unescape or escape string values.

If those are not a problem for you, you can of course use it. The JSONObject provides an iterator so you can simply use a foreach loop to access each element in your array. The following should work

 var json = new JSONObject(www.downloadHandler.text);    
 foreach(JSONObject o in json)
 {
     JSONObject coord = o["coordinates"][0]; // 0 == first nested array inside coordinates
     float x = coord[0].f // first coordinate
     float y = coord[1].f // second coordinate
     int type = o["type"].i;
     JSONObject tags = o["tags"];
     string id = tags["c"].str;
     // ...
 }

Personally i only use my SimpleJSON framework (it also has a JSONObject class ^^). It uses seperate child classes for the different data types json supports. The parser doesn't generate any unnecessary garbage (only the actual structure). It does properly escape / unescape strings and provides many properies to get easy access to the data and to easily convert certain types. It has implicit conversion operators which makes its use quite transparent. It can be used quite similar to the JSONObject:

 // at the top of the script
 using SimpleJSON;
 
 //
 var json = JSON.Parse(www.downloadHandler.text);
 foreach(JSONNode o in json.Children)
 {
     JSONNode coord = o["coordinates"][0]; // 0 == first nested array inside coordinates
     float x = coord[0] // first coordinate
     float y = coord[1] // second coordinate
     int type = o["type"];
     JSONNode tags = o["tags"];
     string id = tags["c"];
     // ...
 }