Fig. 1. Decreasing disks Dⁿ in n-dimensional Euclidean and discrete spaces respectively. The smallest discrete disk Dⁿ consists of point p and (n − 1)-dimensional sphere Sⁿ⁻¹.

Fig. 2. Zero-, one-, two- and three-dimensional spheres S⁰, S¹, S², and S³, and one-, two-, three-, and four-dimensional balls U¹, U², U³, and U⁴.

Fig. 3. If a digital space G is a cone, them the rim O (u) of point u is a cone.

Fig. 4. Normal two-dimensional spheres with a different number of points. All of spheres can be converted into the minimal sphere by contractible transformations.

Fig. 5. Normal spaces with the number of points not more than 6.

Fig. 6. Basic cover of rectangle Y and convex set O, and a digital model of rectangle Y.

Fig. 7. d_ik is the minimal distance between Y_k and Y_i. For any point v in E², there is convex 2-set Y_k such that Y_k contains a solid disk D² of center v and radius r₀.

Fig. 8. (A) A continuous sphere S², (B) a standard cover of a topological sphere, (C, D) two of its smallest covers, and (E) its digital model which is a normal two-dimensional digital space.

Fig. 9. (A) A continuous torus T², (B) a standard cover of T², (C) a cover of T² homotopic to the standard cover, and (D) a digital model of T² which is a normal two-dimensional digital space.

Fig. 10. (A, B) Homotopic covers of a projective plane P². (C) Digital model of P² which is a normal two-dimensional digital space.

Fig. 11. (A) A continuous Klein bottle K², its standard cover, (B) its small cover, (C) its digital model which is a normal two-dimensional digital space.

Fig. 12. Inflation of cover F to cover H.