It is mostly correct. Look at the map.
http://maps.howstuffworks.com/world-mountain-ranges-map.htm
Is this correct? Southern Asia is more mountainous than Northern Asia?
2 answers
The sentence is grammatically correct, but you'd have to be clearer about what you mean as "southern" and "northern" Asia to know if the content of your statement is correct.
http://www.google.com/search?rlz=1C1GGGE_enUS379US379&sourceid=chrome&ie=UTF-8&q=mountains+in+asia
http://www.google.com/search?rlz=1C1GGGE_enUS379US379&sourceid=chrome&ie=UTF-8&q=mountains+in+asia