title: gnuplot: Contour plot of a scattered data set
body: <p>I have a scattered data file composed of 7 columns and more than 8000 thousand lines (<a href="http://speedy.sh/ZhcRX/fort.12" rel="nofollow noreferrer">data file</a>). I would like to plot the contour for this data. The columns I would like to plot are the first one, the second one and the last (seventh) one, giving a 2d and 3d plot as follows:</p>
  
  <p>Front view:</p>
  
  <p><img src="https://i.stack.imgur.com/pGP9K.png" alt="front view"></p>
  
  <p>Edge view:</p>
  
  <p><img src="https://i.stack.imgur.com/A4ouk.png" alt="edge on view"> </p>
  
  <p>And the simple 3d:</p>
  
  <p><img src="https://i.stack.imgur.com/esU1t.png" alt="3d view"></p>
  
  <p>As one can see from the second plot, the first thing is that the points are clustered in a particular location of the 2d region, the same region in which there is the minimum, that can be seen in the 3d plot. But, second, these points are randomly distributed in the plane (second figure) and I guess I cannot use a matrix representation to draw the contours of iso-z.</p>
  
  <p>Is it possible to use gnuplot <code>set contour base</code> and <code>cntrparam levels</code> to do that?</p>