At first, the word "contour" had me pretty confused because I associate it with a curve on a surface. No surface was given, so what "contour" could the OP have meant. Eventually, I realized that the OP probably wanted to see the field arrows emanating from the plane z=0.
Well, early in 2009 I was asked the question "How can a slice of a vector field be graphed?" I answered this in the Maple Reporter's Tips&Techniques article Plotting a Slice of a Vector Field, available in the Maple Application Center here:
In essence, do the following.
There are many options available in the PlotPositionVector command for adjusting the look of the field arrows.
I hope this is what the OP wants.