Isocircles are circles of equal distance from the base location:
The (A) Radius sets the radius of the outmost circle in the account's distance units (miles or kilometers). This radius is then split into (B) Number of concentric circles.
The circles are shown when the base location is set and the (B) Number of circles is set to any non-zero number.
To hide isocircles, clear the base location or set the Number of circles to 0: