This article extends the spatial model of voting to study the implications of different institutional structures of federalism along two dimensions: degree of centralization and mode of representation. The representation dimension varies the weight between unit representation (one state, one vote) and population-proportional representation (one person, one vote). Voters have incomplete information and can reduce policy risk by increasing the degree of centralization or increasing the weight on unit representation. We derive induced preferences over the degree of centralization and the relative weights of the two modes of representation, and we study the properties of majority rule voting over these two basic dimensions of federalism. Moderates prefer more centralization than extremists, and voters in large states generally have different preferences from voters in small states. This implies two main axes of conflict in decisions concerning political confederation: moderates versus extremists and large versus small states.