Mauritania, has the longest border with Mali located in Western Africa.
Nouakchott
Canada.
Miami is a city in the state of Florida in the US. There is no "border" with Miami and another nation.
At 8891 km, the border between Canada and the USA is the longest between any two countries, but a major section of that border (with Alaska) is not contiguous with the rest. The longest contiguous section of border between two countries in the world is between Russia and Kazakhstan, at 6846 km.
California has the longest border with Nevada.
Timbuktu is a city in the West African nation of Mali.
Kentucky has the longest border with Tennessee.
Mali, not Mauritania, is landlocked.
Mali is the nation in Timbuktu.
The longest border in Spain is the border with Portugal to the west. The border with Portugal runs from the north of Spain to the south.
7
Mali