How to normalize markersize to axis in scatter plot?

Hi all,

I want to plot two datasets on a scatter plot. The marker for the first one (say z1) is filled square and colorfilled.

I want to plot the second dataset as circles, whose diameters is adjusted to X and Y axes (which are in fact space). I have tried gca to get the position and all (I have seen it in another thread) but that works only for square markers. Any idea?

here is how it looks like:

scatter(x,y,255,z1,'s'); axis ([0 22 0 40]); xlabel ('X /m'); ylabel ('Y /m'); colorbar;

hold on;

scatter (x2,y2, .....HERE TO MODIFY......)