De Blij, H. J. (1967). Systematic political geography. Wiley.
Lua i Stíl Chicago (17ú heag.)De Blij, Harm J. Systematic Political Geography. New York: Wiley, 1967.
Lua MLA (9ú heag.)De Blij, Harm J. Systematic Political Geography. Wiley, 1967.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.