Contour plots on maps

[Simon de Vet <simon(at)mathstat.dal.ca>]

I have been trying to plot some contour maps onto different map
projections, and for the most part, it is working. I have been having
some troubles, however...

Sometimes, contours try to connect across the map, cutting diagonally
across other lines, instead of terminating at the edges. These lines are
not at the borders of the data, merely at the borders of the current
projection.

I have also had troubles with filled contours on map projections
(Mercator, in my case). While filled plots look nice with no map
projection used, with Mercator they are overwritten with white blocks at
times, leaving only a few spots of colour.  The help says that using map
projections can cause filled contour troubles... Are there any
workarounds?

Thanks

Simon, a new user.