Which areas speak northern dialect in China?

The map shows different areas speaking different dialects in China. The green color shows  70% people that speaking Northern dialect. That means at least 70% people that can understand Northern dialect.

• In the map, the green color show that  people speak northern dialect. 
• Northern dialect is the basis of Chinese dialect, although different areas have their unique pronounce, most Chinese people can understand.

Reference: http://www.chinalects.org/07/publish/funonews.asp?id=1232
                   http://www.somdom.com/general/t2732