51Axx | 49 | 51 | 51B |
| 51A05 | General theory and projective geometries |
| 51A10 | Homomorphism, automorphism and dualities |
| 51A15 | Structures with parallelism |
| 51A20 | Configuration theorems |
| 51A25 | Algebraization [See also 12Kxx, 20N05] |
| 51A30 | Desarguesian and Pappian geometries |
| 51A35 | Non-Desarguesian affine and projective planes |
| 51A40 | Translation planes and spreads |
| 51A45 | Incidence structures imbeddable into projective geometries |
| 51A50 | Polar geometry, symplectic spaces, orthogonal spaces |
| 51A99 | None of the above, but in this section |