How to plot contour at land area only?

I want to show the contour plot only at the land area. I only could plot the boundary line between land and sea and Land+Sea plot (figure A). Is there any simple method that I could, so we can do subtraction between D plot and E plot (figure B)?

D=contour(x,y,zmax')% plot contour both at sea and land
[E,p3]=contour(x,y,-dem',[0 0],'r')% boundary between land and sea

Answer 1

[Etsuo Maeda]

I m not sure what you want to do. But following link will help you to understand the "Relational Operators"

https://jp.mathworks.com/help/matlab/matlab_prog/array-comparison-with-relational-operators.html?lang=en