Georgia is a republic in the Transcaucasus region of western Asia, which includes two autonomous republics—Abkhazia and Ajaria—and one autonomous region—South Ossetia. Georgia's terrain is extremely diverse, and contains high mountain ranges as well as fertile coastal lowlands. T'bilisi is the capital and largest city. With an area of 69,700 sq km (about 26,900 sq mi), the Georgian landscape is dominated by rugged mountain ranges, more than a third of which are heavily wooded. The main ridge of the Caucasus Mountains forms most of the republic's northern boundary, and the highest elevations in the republic can be found there. Climate in the republic ranges from humid, subtropical conditions in the Colchis Lowland to drier and more continental conditions in the eastern uplands.