At the 2009 meeting of the Association for the Study of Higher Education's Council on Public Policy in Higher Education, Pat Callan, President of the National Center for Public Policy and Higher Education, asserted that Master's Colleges and Universities (MCUs) are the most understudied sector of American higher education. This paper described how the 265 public MCUs, which in 2006-7 served 2.5 million students, are for the first time geographically classified in a manner consistent with the 2005 Basic Classification of Associate's Colleges published by the Carnegie Foundation for the Advancement of Teaching. Carnegie's 2005 edition, the first to classify Associate's Colleges, created urban, suburban, and rural sub-classifications that reflect the importance of place in the assignment by states of community college service delivery areas. The proposed public MCU classification is applied using National Center for Education Statistics data on enrollments, institutions, and student financial aid. This is followed by a brief discussion on the use of this geographically-based classification of public MCUs to bring greater precision to postsecondary research, policy, and practice. (Contains 6 tables and 1 footnote.)