In general I don't think the is a 'ideal' answer to this. Mapping multiple dimensions is hard. ("dimension" are a common name for what you are calling 'variable' - ie a specific detail)
So your idea of seperate lists is good for starters.
In fact you are already mapping 3 dimensions. Using x and y coordinates, the location is 2, and then particular variable is the 3rd. You are using colour to represent the 3rd dimension. Three dimensions can be a lot to visually comprehend already
To add more dimensions, one way would be to use a different concept for each. Say different colours for the 1st (non x/y) dimension, size of icon for the 2nd, and altitude above ground (which is possible in GE) for the 3rd. The forth would be something arbitary like icon rotation!?!
the problem with this is 1) your discreet choices y/n/u dont really map well to say altititude or size. Looking at a map of different size icons doesnt like a good way to visually comprehend y/n style choice. (where as say red/green/gray icons makes more 'sense')
2) trying to comprehend multiple dimensions on one map like this would be hard. Very confusing.
A slightly more viable method, is to use in effect 4 icons for each location. Each represent a different dimension. In practical sense this can be done with a single physical icon divided into segments. Each corner can be a different colour, probably a circle or a square. With a bit of patience, should be able to look at this map and comprehend patterns, but it wont be very clear.