We study the set of the representable numbers in base with ρ>1 and n∊ℕ and with digits in an arbitrary finite real alphabet A. We give a geometrical description of the convex hull of the representable numbers in base q and alphabet A and an explicit characterization of its extremal points. A characterizing condition for the convexity of the set of representable numbers is also shown.
 Akiyama, S.Thuswaldner, J. M.2004A survey on topological properties of tiles related to number systemsGeom. Dedicata10989–105.