When we plot this file, consecutive (x,y) points will be connected by a straight line segment. Of course, since we know that this particular line is at z=2, the last coordinate doesn't play any role, but it is listed all the same. What this means is that the 0th contour line is drawn at z=2, and then the (x,y,z) values are listed. We, thus, have just produced the following image. For the actual data points, we use the with image modifier, while for the contours, we increase the linewidth to 1.5, instead of using the default value of 1. When we are done with all this, we simply reset our plot, set the x and yrange, specify the palette that we want to use with the colouring, and call the plot command. We just happen to know that the value of f(x,y) is between -3 and 3, so we set the contour levels at -3, -2.5.2.5, 3. Having written these points into a file, we plot the contour. There will be some 25000 data points in this file, for there are 100 samples (default), and 250 isosamples. In the first couple of lines, we plot the actual function into a file, called test.dat. P 'test.dat' with image, 'cont.dat' w l lt -1 lw 1.5 Set cntrparam level incremental -3, 0.5, 3

If, however, we plot the map through a file, we can use plot, in splot's stead, therefore, the z axis will not appear anywhere in the processing of the plot.ДЄfter this interlude, let us see our first version of the map!ДЇ(x,y)=sin(1.3*x)*cos(.9*y)+cos(.8*x)*sin(1.9*y)+cos(y*.2*x) The reason behind this is that in a 3D plot, we have to have some space for the z axis, and even if we drop it in the map view, the space-holder for the z axis is still there, therefore, gnuplot makes the whole plot a bit smaller. If we plot our function through the file something.dat, then we can use the with image modifier of the plot command, and this means that the plot will be of the same size as would a normal 2D plot. While this might appear superfluous, there are good reasons to do this. This requires a small overhead in terms of scripting, namely, we have got to issue the command One of the advantages of doing this is that in this way, we can make sure that the various plots have the same size. In principle, we could plot both the colour-coded map and the isolines from gnuplot, but we will have much greater flexibility, if we first direct the plots to a file, and then call the data from those files. If you have a matrix to plot, you can replace this function with that file. I don't think that this function has any particular meaning, but it looks quite all right, at least, as far as maps and isolines are concerned. We will produce a simple map using the function As we go along, the map will become more and more complicated, but I hope that I set the right pace, and it will be easy to follow.ДЄ map is nothing but a colour-coded 3D plot, with the isolines attached to it. Since it is simple, this method won't have one of the features, isoline labelling, that the second one has. Well, there is a simple and a not-so-simple way to this. So, you have always wondered how on Earth one can make a real map with gnuplot. Contour plots Maps - Contour plots with labels

Pm3d gnuplot