Gaansager was formerly part of the German Empire. In the German Empire, the place was called Gonsagger.
The place is now called Gånsager and belongs to Denmark.
| Historical place name | Country | Administration | Time |
|---|---|---|---|
| Gonsagger | German Empire | Hadersleben | before the Versailles Treaty |
| Gaansager | Denmark | Tønder | after the Versailles Treaty |
| Gånsager | Denmark | Sønderjylland | 1993 |