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A few potential options if your datasets are both in SQL Server - you could join your two tables in Tableau and use a dual axis map (one axis showing the regions, and one for the sub-regions). You should be able to use the tips here (Dual Axis Mapping - Many Ways ) and look at the spatial file + spatial file section. Starting in Tableau 2018.1, Tableau has direct support for SQL Server spatial data.
You could also union the tables together in SQL Server or with custom SQL in Tableau and then map them (no need for a dual axis map that way)
If you wanted to show points instead, you can just change the mark type to Circle instead of Filled Map, and that will give you the centroid. Alternatively, if you don't like the positioning of the centroids as calculated by Tableau, you could calculate the centroid in SQL Server and read that in as a geographic data type instead of the polygons from your table.