What effect does applying a join in ArcMap have on a layer and a stand-alone table?

Applying a join in ArcMap temporarily combines the attribute data of a layer (such as a shapefile or feature class) with the data from a stand-alone table based on a common field. The correct answer focuses on the nature of this action: it does not create a new output feature class but instead modifies the way the data is viewed during the current session in ArcMap.

The correct choice, which acknowledges that the join will create a new output in terms of how data is displayed, aligns with ArcMap's handling of joins. It effectively appends associated data to the layer's attribute table for the duration of the session, allowing users to analyze and visualize combined datasets without altering the original data on disk.

The concept of a temporary association is crucial, as it illustrates that while users can interact with this combined view, the underlying data remains unchanged unless the join is exported or specifically saved, which is not implied in the choice provided.

The other choices suggest either permanent changes or creating new structures that do not accurately reflect the functionality of joins in ArcMap, which operate by temporarily modifying the view of the data, not altering the underlying datasets or creating new physical files unless additional steps are taken.