Bit of a complicated one but I'll explain what I'm trying to achieve and the ideas I've had to solve it and why they won't work!
I have two maps with custom polygons on (attached) which you can change between on a separate Dashboard (filter between two different levels of geography). Now after you've selected a geography there is another filter which selects an area within that geography and carries across to all other pages. I don't want the filter to actually filter the map, I want this area to be a different colour, so i've had to create a parameter which then feeds into a calculated field for colour. This works fine but using a parameter with a list of the areas means i can't make the list change depending on which level of geography is chosen. For the first level (Local Enterprise Partnership) there are 39 areas and the second level (government region) there are 9, so ideally the user would select LEP, choose from 39 options and see the selected LEP be a different colour on the map, and if they select region, see a list of 9 regions and so on. I then want this parameter to act as a filter for the remaining pages of the document
As far as I'm aware I have several not very elegant solutions...
Make the geography filter into a parameter which gives you one of two lists (so two more parameters) which are on top of each other, and depending on the selection, one disappears leaving the other one to select from.
Making two separate parameters side by side and just ask the user to select one from the right list
Use a region filter as an exclude value so that once you've selected it that region disappears leaving all the others visible.
Is there a better more elegant way of getting this result or is it just not worth the effort?
You may want to consider using a duplicate datasource for your filtering rather than a parameter. Check out this blog posts for hints and then generalize to your specific needs. Maintain percent of total in Tableau when using filters