The set of space-filling curves: Topological and algebraic structure

In this paper, a study of topological and algebraic properties of two families of functions from the unit interval I   into the plane R2R2 is performed. The first family is the collection of all Peano curves, that is, of those continuous mappings onto the unit square. The second one is the bigger set of all space-filling curves, i.e. of those continuous functions I→R2I→R2 whose images have the positive Jordan content. Emphasis is put on the size of these families, in both topological and algebraic senses, when endowed with natural structures.