Yankes doesn't try to draw circles, he simply modifies his shading which totally re-renders whole globe. And I was saying about colored lines drawn over globe, like borders between countries. There is already "tab" button which toggles border view, and we could add some other button for toggling radar circles.
Personally I'm against toggling between day-night and radars, because when watching UFOs flying through radar coverage zones, you just leave night/day line out of control. Specially when chasing ufo craft for some reason in background.
And actully this is unnecessary to get into full rerender just because of radar ranges. It would be a waste of resources.