COncerning finding the domain of functions in two variables, I'm unsure as to how to sketch the graph of an equation with two square roots. i have sketched the graph of the domain of each of the terms simple enough for this function:

f(x,y)= (sqrt(4-x^2-y^2)) - (sqrt(1-x^2))

i end up with a circle for the first term and a parabola for the second. when i sketch the graph of the domain of the entire function, should i get the intersection? or just put one sketch on top of the other? please help. thank you