This paper presents necessary and sufficient conditions for the existence of homomorphisms for equidistance relations in terms of the closed subsystems (the Fundamental Theorem of Homomorphisms). Further, it shows that every closed subsystem of a 1-point homogenous equidistance system is a coset of a unique homomorphism. Affine spaces and other incidence geometries can be seen as examples of equidistance systems.
Sibley TQ. 1983. Homomorphisms for equidistance relations. Cuttington Research Journal 2(1): 1-11.