Gnuplot question: how to plot 3D points as colored points in map view?

I have a simple gnuplot question. I have a set of points (list of x,y,z values; irregularly spaced, i.e. no grid) that I want to plot. I want the plot to look like this:

  • points in map view (no 3D view)
  • color of each point should depend on its z-value.
  • I want to define my own color scale
  • plot should contain a little legend box in the form of a color bar listing what z-value corresponds to what color

I tried pm3d, but it seems it only handles gridded data, i.e. x,y's on a regular grid, or at least displays them as such. I just want to see the individual points (no interpolation).

Thanks for your help here.