Thailand, an area of about 200,000 square miles in the heart of Southeast Asia, stretches from latitude 5 30" North to 21 North, or not quite 1,000 miles. The longitudinal extent is half this distance, from 97 30" East to 105 30" East. It thus falls entirely within the tropical climate region. The country is bordered on the north-east by Laos, on the south-east by Cambodia, (these two countries, together with North Vietnam and South Vietnam, comprising the area once known as French Indo-China,) on the south by the Gulf of Thailand and Malaya and on the north-west and west by Burma. The whole country is made up of river plains, forested mountains, and plateaus. It is a tropical land where rice cultivation in the river basins is the primary mode of existence for its approximately 25.5 million people.