Geographic Spines in the 2020 Census Disclosure Avoidance System TopDown Algorithm
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The TopDown Algorithm (TDA) first produces differentially private counts at the nation and then produces counts at lower geolevels (e.g.: state, county, etc.) subject to the constraint that all query answers in lower geolevels are consistent with those at previously estimated geolevels. This paper describes the three sets of definitions of these geolevels, or the geographic spines, that are implemented within TDA. These include the standard Census geographic spine and two other spines that improve accuracy in geographic areas that are far from the standard Census spine, such as cities, towns, and/or AIAN areas. The third such spine, which is called the optimized spine, also modifies the privacy-loss budget allocated to the entities within the geolevels, or the geounits, to ensure the privacy-loss budget is used efficiently within TDA.
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