Which action causes a change in schema?

When discussing changes in schema within a Geographic Information System (GIS), it is essential to understand that schema refers to the structure of the database, including the tables, fields, and their relationships. This means any action that alters the organization, field types, or overall structure of the data can be considered a change to the schema.

Deleting a field directly impacts the schema since it involves removing a component that defines part of the structure of the dataset. This action alters the database's design by reducing the number of attributes associated with a feature, thereby creating a different schema than previously existed.

On the other hand, digitizing a new line, changing the shape of a polygon, or updating an attribute value all involve modifications to the data contained within the existing schema rather than altering the schema itself. These actions maintain the framework of the database but modify the existing data or geometry, so they do not result in a schema change.

Thus, deleting a field is the action that fundamentally alters the underlying structure of the GIS data, which is why it is recognized as causing a change in schema.