Layering filled maps and polygons on map (2018.1 update)

I wrote about this technique more than a year ago and it was one of my more popular posts, thanks to a tweet by zen master Chris Love. It is time to update the particular example as version 2018.1 finally brings generated Latitude and Longitude closer to Latitude and Longitude already in the dataset.

We start by UNIONing our two sources, the polygon source having latitude and longitude, the mark source having a field that can be interpreted as a filled map.

 We then use the new trick of putting generated latitude and longitude on the axis, with source latitude longitude in the level of detail for the polygon layer. In the past I would import the filled map source, generate the latitudes longitudes, export crosstab to excel, save as csv, and do a union with the polygon csv. No longer necessary as of 2018.1.

Now all that is required is dual axis to overlay the polygon over the filled map.