The rough dividing line between North and South China (at least "China Proper") is the Yangtze River, officially referred to as the Changjiang ('Long River') in Chinese. Unlike the Mason-Dixon line in the U.S., this division in China is the result of natural geological forces, not the result of any artificial human compromise. Like the Mason-Dixon line, however, the boundaries get fuzzier the farther you go west. (See maps; scroll down.)
South of the Yangtze, people depend mostly on rice as their staple, they prefer black tea, and they generally get by without heating their houses during the winter. (The coldest winter I ever spent was in one of those unheated houses in South China. Another foreign family there made the same claim--and they were from Winnipeg, Manitoba!) The old southern capital, Nanjing ('South Capital') lies on the south bank of the Yangtze. (See maps and photos; scroll down.)
North of the Yangtze, people grow a variety of hardy staples such as wheat, corn (maize), sorghum, and millet, which they make into pastas, breads, or gruel. They prefer green tea, and they generally do a better job of heating their houses during the winter. (See maps and photos; scroll down.)
In popular stereotype, the North has more than its share of hardheaded ideologues, while the South has more than its share of unprincipled pragmatists. However, the pragmatic leader Zhao Ziyang was a northerner from Henan (although he rose to prominence in Guangdong), while the arch-ideologue Mao Zedong was a southerner from Hunan. The smooth diplomat Zhou Enlai was from Jiangsu, which straddles the Yangtze. (See maps of major provinces.)
If bureaucratic Beijing ('North Capital') is the northern archetype, hustling Guangzhou ('Wide State') is its southern counterpart. (See map of major cities.) Shanghai, at the mouth of the Yangtze, has a reputation for combining both ideological and mercantile hustle. Shanghai literally means 'rise-up sea', which may originally have meant 'the beginning of the sea' (and the end of the river), but I can't find any confirmation.
Unfortunately, many Cantonese seem to think that the North starts at the northern border of Guangdong Province--or that you have to speak Cantonese to be a southerner. Several of the teachers at the brand new college we taught at in Zhongshan City, Guangdong, were from Jiangxi Province, which stretches from Guangdong north to the Yangtze. They were frequently dismayed to be identified as beifangren 'northerners' when they spoke their southern dialect of the national language (putonghua, or Mandarin) rather than Cantonese. To Cantonese, they were just not southern enough. It was like Georgians calling Virginians--or Mississipians calling Tennesseans--"Yankees"! (Hmm. Come to think of it ...)
Recommended Browsing: A Visual Sourcebook of Chinese Civilization.