51Exx Finite geometry and special incidence structures
 51E05 General block designs [See also 05B05]
 51E10 Steiner systems
 51E12 Generalized quadrangles, generalized polygons
 51E14 Finite partial geometries (general), nets, partial spreads
 51E15 Affine and projective planes

51E20 Combinatorial structures in finite projective spaces [See also 05Bxx]
(1)
 51E21 Blocking sets, ovals, karcs
 51E22 Linear codes and caps in Galois spaces [See also 94B05]
 51E23 Spreads and packing problems
 51E24 Buildings and the geometry of diagrams
 51E25 Other finite nonlinear geometries
 51E26 Other finite linear geometries
 51E30 Other finite incidence structures [See also 05B30]
 51E99 None of the above, but in this section