Asymptote is an excellent software for scientific drawings.
But the contour plotting is still not implemented. I
have tried to write subroutines to do the job, but
finally I gave up.
Would you please consider to add this functionality in
the future releases? I think some features could be
considered, such as drawing the isolines using
different pens, filling the area between the isolines
using different colors or patterns, labeling the
isolines by values or custom labels, legends, etc.