First of all, I would like to thank both of you (@Markiyan Hirnyk and @Preben Alsholm) .
The reason is that I use another software for just plotting purpose,
which gives me a very nice visual results.
The problem is that the output produced by maple is not that good
(maybe bcoz of my lack of understanding).
Forexample
contourplot(p(x)(y),x=-4.0..4,y=-1.5..1.5,grid=[100,100]);
Here you can see, the output is not that clear. And I do not know how to choose
a more visible color and also how to change the labels and to make it more bright.
P.S. As you mentined about the "connecting lines", bcoz of that I can not use the
data more freely (restricted to point style).