Even though your challenge is not on a geographic map, I believe the issues are the same as I describe in Mapping polygons and points together dual axis.
I believe the most significant piece of this puzzle is the data set. I believe you need a UNION rather than a JOIN. Since Tableau cannot perform a UNION, this needs to be done outside of Tableau, and then follow the steps described in the above document.
Does that help? If not, let me know what your challenges are, and I'll try to help further.