1. What is the center of an area or the center of a population;J. W. Hayford;Journal of the American Statistical Association,1902
2. Weber A. (1909). Über den Standort der Industrien. Mohr.
3. Mathematics and the picturing of data;J. W. Tukey;In Proceedings of the International Congress of Mathematicians,1975
4. Descriptive statistics for multivariate distributions;H. Oja;Statistics & Probability Letters,1983