A little tricky, but doable.
First, create a map using whatever field you have (e.g. State). Then, duplicate the 'Latitude' field and put it on the same Rows column. Right-click the 2nd field, and choose 'Dual Axis'.
Then, on the Marks shelf, click on the carrot in the upper-right corner, and select 'Multiple Mark Types.' Then, click on the arrow next to 'All' to the first 'latitude', and select Filled Maps. Then go to the second 'latitude' and select Pie (all of this on the Marks shelf).
Pictures attached. Let me know if that works for you!
Thanks, that's exactly what i was looking to do too! It works nicely for me, but the pie charts are appearing behind the colour coding for the heat map so look washed out. Would you know how to bring them to the front?
Seth, try swapping the two lat pills on the row shelf. It should bring the pies to the foreground.
Thanks Shawn, I had that Eureka moment this was probably the solution half an hour after putting it down. Now trying to figure a way for the user with Reader to manually change the size of the pies, which unless i am again missing something obvious, is not straightforward. I've tried experimenting with calculated fields e.g. creating a measure unrelated to the data and returning a value based on a filter selection, which is then used in the size pill, but the implementation eludes me.
Try a parameter that is then used in a calculated field which also makes use of whatever you are currently sizing the pies on, and put that field on the Size shelf and the parameter in the view for users to manipulate.