You need to ensure that the Sales Per Capita calculated measure produces correct results. What should you do?

The DataType property on the column in the data source view does not directly govern how SSAS reads the measure's source values - the measure's own Source DataType property takes precedence.

The Source DataType property on an SSAS measure tells the Analysis Services engine how to interpret the raw column data from the underlying source. If the Population measure's Source DataType is set to a smaller integer type, large values can overflow or be truncated before the division occurs in the Sales Per Capita expression. Setting Source DataType to BigInt ensures the full precision of the population values is preserved during measure evaluation.

Changing the physical data warehouse column type is an ETL/database layer change and does not by itself correct how SSAS interprets or processes the measure's data type within the cube.

The DataType property of the measure controls the output format returned to clients, not how source data is read; it is the Source DataType that determines how incoming data is interpreted by the engine.