Thank you for the answers but I just realized that it does not matter since the data points I have do not represent a function of two variables. It is just a list of triples satisfying a certain condition in the form f(x,y,z)>0. So, in fact, it is more like a function of three variables. The easiest thing is to fix one of the coordinates and plot the region determined by the rest and so on. I wanted to delete my question when I realized this but I can't find a way to do this.