Let K be a maximal arc with degree d. Consider the incidence structure , where P contains all points of the projective plane not on K, B contains all line of the projective plane intersecting K in d points, and the incidence I is the natural inclusion.
Let K be a maximal arc of degree d within the projective plane. The incidence structure is defined by two sets: P, containing all points not on K, and B, containing all lines intersecting K at d points.  The incidence relation I maps each point in P to every line in B.