I just want to suggest that the straight line segments in
contours actually serve a useful visualization purpose.
Straight segments tell you that you have zoomed in far
enough that there are no longer underlying data points in
the region covered by the screen, and that the visible
contours are interpolations between a few data points that
lie beyond the screen edge. Smoothing the lines into curves
hides this information from users. Consider the following
wonderful quote from Mark Twain:
I was gratified to be able to answer promptly,
and I did. I said I didn't know.