Actionscript 3 :: Way To Store And Retrieve A Map Data?

here's the thing, i need to store different values in a 2d array (or something conceptually similar). The idea is to create a 2d map with tiles and the array would save the ID of every tile in the map. I'm trying to create something mildly efficient, specially because i need to save some memory usage for later use (it has to do with AI) and it must run on a low end PC, but simply creating an array seems to be a waste of space since i only have about 50 different IDs at any given map.i thought about creating a 2d array of 8bit chars would be sufficient, but that's out of the question with actionscript 3, it doesn't have 8bit char data type.