A famous theorem on space-filling curves is the Hahn-Mazurkiewicz theoremHahn-Mazurkiewicz theorem: Let X$X$ be a Hausdorff space, then there exists a surjective continuous map [0,1] \to X$[0,1] \to X$ if and only if X$X$ is compact, connected, locally connected and metrizable.
Is there a similar characterisation for all (Hausdorff) spaces having a surjective continuous map into the unit interval (which I decided to call line-filling spaces)?