Explanation
Refer section "Null values appear after blending data sources" at
https://help.tableau.com/current/pro/desktop/enus/
multipleconnections_troubleshooting.htm

Create an inner join between Orders and Returns table using Order ID
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Create a calculated field to find the unique order.
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Drop Region, Ship Mode, and Category to Rows. And drop 'countd order' field to Text. The final view would look like this:
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Drop Order Date to the Columns and change it to continuous month. Drop sales to the rows.
Go to Analytics and drop the trend line. Check for all trend lines, Linear is having the lowest R Square.
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Drop the Latitude and Longitude fields to Rows and Columns shelf respectively. Or double click on these fields.
Drop the Location field to Filter shelf, select the Location as Colombia.
Drop the Name field to the Label.
To show the cities go to the Map -> Map layer and Check the Cities.
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Drop the Deaths and Year fields to the Tooltip. Now your view looks like this:
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Zoom-in the map, you will find Purace is the nearest one in the Popayan city and Dona Juana was having 55 deaths.
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You cannot mix the aggregated and non-aggregated calculations.
MAX(SUM(Profit), (Sales)) -> Profit is aggregated but Sales is not.
SUM([Profit]) * [Quantity] -> Profit is aggregated but Quantity is not.
You can multiply the aggregated/non-aggregated fields with constant. That's why SUM([Profit]) * 1000, is correct.
SUM([Profit]) * SUM([Quantity]) - Both are aggregated