Original 11-dotted line map published by Republic of China in 1947. In 1950s People’s Republic of China removed 2 dotted lines in the area of Gulf of Tonkin after it reached an agreement with Vietnam. Since then map is referred to as 9-dotted/9-dash/U-shaped line.
Source: Wang, K.H. (2010). The ROC’s Maritime Claims and Practices with Special Reference to the South China Sea. Ocean Development & International Law, 41(4), p. 244. doi:10.1080/00908320.2010.499282
Map attached to Chinese note verbale to UN in protest against joint Malaysia-Vietnam submission to Committee on the Limits of Continental Shelf (May 2009)
Source: Dutton, P. (2011). Three Disputes and Three Objectives: China and the South China Sea. Naval War College Review, 64(4), p. 46.
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Notice how indiscrimate and inconsistent that U-shaped line is.
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