The Space Mapping page of the Schema Wizard is displayed when you select the option to include physical table/indexes layouts into the generated schema or sub-schema.
If some source database tables or indexes are explicitly placed in particular DB or BLOB spaces or have a fragmentation, your target platform should have matching spaces to be able to run the generated schema script.
This page of the wizard gives you the opportunity to map the source spaces to existing target spaces if their names are different from the source.
To map the space, when you selected the Export to Script File target option, type in the Target column of the grid the new space name for each source space.
To map the space, when you selected the Deploy to Another Database target option, choose the existing target space from the dropdown list in the Target column of the grid.
The generated SQL script file will contain new space names.