When it comes to family arrangements, the United States has a North-South divide. Children growing up across much of the northern part of the country are much more likely to grow up with two parents than children across the South. It’s not just a red-blue political divide, either. There is a kind of two-parent arc that starts in the West in Utah, runs up through the Dakotas and Minnesota and then down into New England and New Jersey. It encompasses both the conservative Mountain West and the liberal Northeast. Single-parent families, by contrast, are most common in a Southern arc beginning in Nevada, and extending through New Mexico, Oklahoma and the Deep South before coming up through Appalachia into West Virginia. These patterns — which come from a new analysis of census data — are important because evidence suggests that children usually benefit from growing up with two parents. It’s probably not a coincidence, for instance, that the states with more two-parent families also have higher rates of upward mobility. Talking about the advantages of two-parent families can be awkward, I realize, because it can seem to dismiss the heroic work that so many single parents do. Managing parenthood, work and the rest of life without a partner is deeply impressive. Nevertheless, the sharp rise in single-parent families has contributed to sky-high inequality and deserves discussion. The new geographic analysis comes from W. Bradford Wilcox, a University of Virginia sociologist, and Nicholas Zill, a psychologist. They did the analysis, they said, after reading recent Upshot articles on upward mobility and marriage — and realizing that the geography of American family was somewhat different from the conventional wisdom. That conventional wisdom stems from the fact that politically conservative states, for all their emphasis on family values, have long had high divorce