Abstract: The Census will deploy a "differentially private" disclosure avoidance mechanism for its 2010 Decennial release. That is, it will intentionally introduce random noise to all the numbers that are released! But in a controlled way that you can prove theorems about. This is causing elation in some circles (e.g., CS departments) and panic in others (e.g., community organizers and voting rights litigators). I'll describe a mathematical exploration of the Census's TopDown algorithm with an eye to the use case of redistricting. This is joint work with Aloni Cohen, JN Matthews, Bhushan Suwal, and Peter Wayner.