It's an n-dimensional spectra, but I'm not really sure what n is in this case. It's at least two, with one dimension being masculine/feminine and the other being penis/vagina, but there are way more things to sexual preference than that. We need one for dominant/submissive, multiple dimensions for hair color, maybe age, and all kinds of other factors. Every person will have a range of preference for all of these, and they aren't just the far ends.