CONTOURSPLINE(X,Y,Z,N) creates a contour plot having N contour levels from the matrix Z, treating the values in Z as heights above the X-Y plane. X and Y are either vectors defining the X- and Y-axes with length(X) = size(Z,2) and length(Y) = size(Z,1), or X and Y are matrices the same size as Z such as those produced by MESHGRID.
CONTOURSPLINE(X,Y,Z,V) draws contours at the levels given in vector V.
CONTOURSPLINE(X,Y,Z,[v v]) draws a single contour line at level v.
Beware: CONTOURSPLINE smooths contours, but does not magically change terrible data into pleasing data. For terrible data, smoothed contour lines may cross!