Well... If your world is procedurally generated, your procedural algorithm should probably populate your array as you go.
If you want to load an array you create manually, you can create it in your spreadsheet program of choice, save as .csv, import that with the AJAX object, then use tokenat to break it up and load it into your array.
If you're looking for an algorithm to procedurally generate terrain... I'm not much help there but I'm sure there are a ton of tutorials and examples online.
JSON strings are created from already-populated arrays - you can use Array.asJson to get the contents of the array all in one string, in JSON format. You can then save this string and load it back into an array later.
Mistakes were made.