 Solution

For a nonzero level $h$, completing the square givesThus the level sets of a linear numerator over a radial quadratic are circles centred on $y=x$, real only for $0<|h|\le 1/\sqrt{2}$. The extreme levels shrink to points. The zero contour is the straight line $x+y=0$, separating positive and negative heights; near it, small nonzero levels are large circles. Heights tend to zero at infinity.