1. National Oceanic Service, WWW document, (How much oxygen comes from the ocean? (noaa.gov))
2. E. Motivans. The Different Types of Forests. Everything You Need to Know, WWW document, (The different types of forests: everything you need to know (zmescience.com))
3. MyBIS, Malaysia Geographical, WWW document, (https://www.mybis.gov.my/art/143)
4. Jabatan Perangkaan Malaysia, WWW document, (https://www.dosm.gov.my/v1_/)
5. H. Abdul Rahman, MJEM., 10(2), 17 (2009).