I'm not 100% sure what you mean by "Fictional Spaces", pretty broad term but anyhow, there is Campaign Cartographer which seems to be the standard for dedicated map-making solutions on a grand (regional/continental) scale, I think there are also sub-applications like city Cartographer etc. Personally, I only use Photoshop for it's flexibility. There is a very active online community centered around all aspects of map making, the
Cartographer's Guild.