During the 19th century wards were used by the Census Bureau for data at the level below cities. This was problematic as wards were political subdivisions and thus changed after each census, limiting their utility for comparisons over time. Census tracts were first used in Chicago in the 1910 Census. However, by the 1920s the Social Science Research Committee at the University of Chicago wanted divisions that were more natural and manageable than the arbitrarily-designated and numerous census tracts. The sociologist Robert E. Park led this charge, considering physical barriers such as railroads and the Chicago River to form distinctive and consistent areas within the city, which he deemed "natural" areas that would eventually merge into a distinctive identity. Ernest Burgess, a colleague of Park's who shared his thinking, was crucial in creating and naming the community areas. Initially able to identify 400 neighborhoods of the city, he considered that number excessive and trimmed it down to 80 and thereafter 75 by grouping related neighborhoods into a single community area. The Chicago Department of Public Health wished to present local differences in birth and death rates; it worked with the committee to produce the list of 75 community areas, which were divided into 935 census tracts.