Official Gazette: ACT NO. 2657 AN ACT CONSISTING AN ADMINISTRATIVE CODE CHAPTER 2 Political Grand Divisions and Subdivisions.
Ignacio Villamor, Director: Census of the Philippine Islands taken under the Direction of the Philippine Legislature in the year 1918. Volume I Geography, History, and Climatology. Compiled and published by the Census Office of the Philippine Islands. Manila, Bureau of Printing, 1920.