docs: def create_point(self, xcen, ycen, size=10, color='red', fill=None):
          """Plot a circle of size at this x,y location"""
  
          if fill is None:
              fill = color
  
          (x, y) = self.p2c((xcen, ycen))
          x1 = x - size
          x2 = x + size
          y1 = y - size
          y2 = y + size
          self.create_rectangle(x1, y1, x2, y2, fill=fill, outline=color)