circle [ item <id> ] [at] <vector> radius <length> [ with { <option> } ]
The circle command is used to draw circles on multiplot canvases. The coordinates of the circle’s center and its radius are specified. The with modifier allows the style of the circle to be specified using similar options to those accepted by the plot command. The example
circle at 2,2 radius 1 with color red fillcolor blue
would draw a red circle of unit radius filled in blue, centered 2 cm