SPATIAL SCIENCE 89 Vol. 54, No. 2, December 2009 Estimating Components of Population Change from Census Data for Incongruent Spatial/ Temporal Units and Attributes R. G. Cromley A. Y. Ebenstein D. M. Hanink R. G. Cromley Department of Geography Campus Unit 4148, 215 Glenbrook Rd. University of Connecticut Storrs, CT 06269-4148 robert.cromley@uconn.edu Avraham Y. Ebenstein Institute for Quantitative Social Science Harvard University Dean M. Hanink Department of Geography University of Connecticut When calculating the components of population change over time, the spatial units of analysis must remain constant. However, the boundaries of these units often change from one census to the next. Another limiting factor is the absence of data values for the time period. Net migration figures might be available for a five year interval in a census but not for a twenty year interval. GIS and areal interpolation are used here to rectify boundary changes that occur from one census to the next and shift-share analysis is used to estimate the components of population change from the census data. These methods are applied to a county level study of population change in China between 1982 and 2000. Keywords: Population change, misaligned data, shift-share analysis, census, China. INTRODUCTION Census data are probably the most readily available form of demographic data for many countries but have limitations in the context of temporal studies. Many population studies involve comparisons between the population characteristics of a region for two or more dates as well as the calculation of rates of change in these characteristics over the intervening interval. In order to calculate the components of population change between two dates, however, the spatial units of analysis must remain constant in their geography; otherwise the same regions are not being compared. However, the boundaries of administrative units used to collect population data in a census are often changed during the time interval of interest. This is a common problem in the United States where census reporting units such as tracts are redesigned to reflect the growth of certain areas, and in developing countries such as Nigeria and India where new political units are added over time to recognize different ethnic groups.