Horse on road and field

homage a I.M. Gelfand Read the problem in the right hand panel. You can move the horse down the road by dragging the BLACK dot. You can see the region the horse can reach from this point on the road by clicking on the check box. The Field point will be RED if that point can’t be reached within the hour from the position on the road. The Field point will be BLACK if that point can be reached within the hour from the position on the road. What is the shape of the region that the horse can reach within one hour after leaving the barn? Can you calculate the area of this region?