I have been writing a Python program to analyze the contents of shapefiles from the 2010 U.S. census, and I came across some odd duplication that I cannot explain. For example, in the 2010 shapefile data that describes census tracts in the state of Texas, shapeRecord(546) part 0 has a list of geographic points of a polygon that are identical to shapeRecord(547) part 1. These records correspond to geo ID 48159950200, Census Tract 9502 Franklin County, TX and geo ID 48159950100, Census Tract 9501, Franklin County, TX, respectively. This seems to suggest that the first part of census tract 9502 geographically overlaps with the second part of census tract 9501, and the corresponding population data shows that they have different populations.
Has anyone studying census shapefiles encountered such anomalies, and do they know what it means? Is it possible that the census counts the population of the same geographic area by different means and then assigns part of the population to one tract and a different part of the population to another tract?