Urban-Rural Definition Classification System
CSN uses the urban-rural classification system developed by the National Center for Health Statistics (NCHS). To show how injury rates vary by level of urbanization, a table based on the classification system appears below and defines six levels of urbanization: large central metro, large fringe metro, medium metro, small metro, micropolitan, and noncore.
1 There must be at least one large central county in each large metro area. Source: http://wonder.cdc.gov/wonder/help/CMF/Urbanization-Methodology.html