Where in the world?
The flag of Mauritania has a green field with a gold star and crescent in the center, and two red stripes at the top and bottom.

Mauritania

موريتانيا

Population: 4,649,660

Region: Africa

Subregion: Western Africa

Capital: Nouakchott

Top Level Domain: .mr

Currencies: Mauritanian ouguiya

Border countries

The flag of Algeria has two vertical bands of green and white, with a red crescent and star centered over the boundary between the colors.

Algeria

Population: 44,700,000

Region: Africa

Capital: Algiers
The flag of Mali has three vertical stripes of green, yellow, and red.

Mali

Population: 20,250,834

Region: Africa

Capital: Bamako
The flag of Senegal has a green, yellow, and red vertical tricolor with a green star in the center.

Senegal

Population: 16,743,930

Region: Africa

Capital: Dakar
The flag of Western Sahara has a horizontal tricolor of black, white, and green with a red triangle on the hoist side.

Western Sahara

Population: 510,713

Region: Africa

Capital: El Aaiún