When you create a new schema comparison project and you select your data sources, Schema Compare automatically maps objects with the same name and schema for you.
In case you need to compare objects having the same name, but belonging to different schemas, you can map the schemas as the circumstances require. For example, if you want to compare objects in a test database that are owned by HR with objects in a production database that are owned by Staff, you can map HR to Staff.
You can edit mappings on the Schema Mapping tab of the New Schema Comparison wizard.