[Gnuplot-info] How to plot a colored distribution map?

[Xi L. <jas...@gm...>]

Hi all:
I got a 3 dimension data set whose x and y values both range from 1 to 200,
z value varies between -5000 to 5000,  I want to plot a 2d colored
distribution map drawing 40000 points with different color depending on
their z value, for example the point with -5000 get pure white, and 5000 get
pure black, and the color will change smoothly from . So I can tell where
the most black area goes during plotting several consecutive date sets and
decide which x,y pair I should use in the future.
But I don't find corresponding command to solve my problem, so I use the
following commands:

set palette model RGB defined (0 'white', 1 'black')
set view map
splot "file"  u 1:2:3 with points palette

a stupid solution, draw the 3d picture and look down from above. this kind
of solve my problem except the picture are not that smooth and points are
cross-shaped. I think I must have missed some important command in gnuplot,
would someone give me a hint how to solve this in a gnuplot way?

and BTW, when I open there pipes to three gnuplot processes  issuing
 commands plotting the pictures I described above, the whole process takes
about five seconds to draw the whole 3 pics. Is that a little abnormally
slow?

Thanks for your time on my stupid question.