The atlas data are stored in a SQLite 3 database.
see the Atlas Database page.
The panel below the input field shows if the selected file is valid.
The atlas database can be imported from a SQL file.
The default import file is located in the directory "atlas/geonames1000.sql". It contains an extract of the geonames.org
atlas DB (worldwide cities with more than 1000 inhabitants).
Supported import formats are
SQLite 3 dumps in plain SQL format
Zipped SQLite 3 dumps
The import can be canceled while running. The database will quite likely be invalid then.
Backups are stored according to the configuration in the General Configuration tab (no backup/single backup/infinite backups).