Which action is necessary to link a Country field as geo data in relationship with a City field?

Establishing a clear relationship in the data model is essential for effective data visualization and analysis. When linking a Country field to a City field, it is crucial that these two fields are properly related within the data model. This ensures that the system understands how these two geographical dimensions correspond to one another.

By creating this relationship, the mapping process is facilitated, allowing for accurate geo-data representation, where cities can be displayed in context to their respective countries. This relationship enables effective aggregations and insights into geographic analysis, providing users a coherent understanding of the data.

The other choices do not address the fundamental need for a structured relationship between the two fields. Without this relationship, even if the fields exist or are formatted correctly, the system would struggle to utilize the geographical data effectively.