The Regions: Mainland And Maritime and Wallace line

Geographical

Southeast Asia is geographically divided into two regions, namely Mainland Southeast Asia (or Indochina) and the Maritime Southeast Asia (or the Malay Archipelago) (Indonesian language: Nusantara).
Mainland Southeast Asia includes:
Cambodia
Laos
Myanmar
Thailand
Vietnam
Maritime Southeast Asia includes:
Brunei
East Timor
Indonesia
Malaysia
Philippines
Singapore
The eastern parts of Bali Island between Lombok Island is Wallace Line which is considered to be geographically parts of Oceania.
The Andaman and Nicobar Islands of India are geographically considered part of Southeast Asia. Bangladesh and the Seven Sisters in India is culturally Southeast Asia and sometimes considered both South Asian and Southeast Asian. Hainan Island and several other southern Chinese regions such as Yunnan, Guizhou and Guangxi are considered both East Asian and Southeast Asian. Taiwan, which sits on the Tropic of Cancer and borders the South China Sea, is likewise often included in definitions of Southeast Asia as well as East Asia. The rest of New Guinea is sometimes included so are the Federated States of Micronesia, Palau, Guam, and the Northern Mariana Islands, which were all part of the Spanish East Indies and will be considered Oceania.