Base R has a function for plotting circles called "symbols". Unfortunately, the size of the circles is inconsistent across devices. This function plots circles whose radius is specified in used coordinates.
circles(x, y, radius, bg = NULL, fg = "white", ...)centers (x coordinate)
centers (y coordinate)
radius (in user coordinates)
background colour
foreground colour
passed to polygon, e.g. lwd
none, used for side effect
hough_circle