Custom geocoding means you assign latitude and longitude coordinates to your locations so Tableau can plot them accurately. It also allows you to form custom geographic roles that you simply simply can use as you create map views in Tableau.
Step 1: Create a CSV file along side your location data
The first step to custom geocoding your data is creating a CSV file to import into Tableau. The contents of this file differ relying on whether you’re extending an existing geographic hierarchy, adding a replacement geographic role, or adding a replacement hierarchy to Tableau.

However, the next applies to all or any or any custom geocoding files:

The .csv file must contain Latitude and Longitude columns.

Extend an Existing Role
The built-in geographic roles in Tableau contain hierarchies which can be extended to include locations relevant to your data. as an example , the prevailing hierarchy of Country > State/Province won’t contain all of the states or provinces in your data. you’ll extend this level to include missing states or provinces.
the column names must match the prevailing geographic roles within the hierarchy that you simply simply are extending. this might confirm that the new locations are added to the proper roles and hierarchies.