In lieu of any official definition of “urban population” in Thailand, researchers and policy makers have generally used a simple urban-rural dichotomy, relying upon the administratively designated municipal areas as urban and the remainder of the kingdom as rural. For administrative purposes, however, a more refined set of residence categories is available: the “urban” segment is subdivided into three categories of municipal areas; within the “rural” group, units of population concentration classified as sanitary districts are distinguished from the remainder of the rural population. Data from a 1970 census sample tape have been used to analyze a number of socioeconomic characteristics, as well as migration and fertility, for each of these five residence categories separately in an attempt to determine if the formerly used rural-urban dichotomy is valid. For each of the characteristics and for migration and fertility, a clear urban-rural continuum emerges, with the sanitary districts generally resembling the smaller urban places more than they do the rural areas under which they are usually subsumed. The evaluation thus suggests the importance to research and policy either of using an urban-rural continuum or of grouping sanitary districts with municipal areas when a dichotomy must be used. Doing so should facilitate evaluation of the interrelations between urbanization and demographic and development factors.