Newbie question plotting x y data

I have a very silly question: I have data in the format

x y data(x,y)

and now I would like to plot a point with a color corresponding to
data at position x,y (pretty much like with imshow). Unfortunately,
the data does not always fill a rectangular grid, so that using imshow
just as it is, does not work. What is the best method to do this in

Thanks in advance,


Hanno Klemm