I want to do kernel smoothing on the standardised mortality rates at
specified location(x-y coordinates) and be able to produce contour map.
I've tried to use the package called fields in R (function smooth.2d)
but the problem is I get negative results after smoothing and I do not
understand why? Your contributions will be highly appreciated or if
there is any package that can do this I will be happy to know about it.
Thanks in advance for your comments.