The preternaturally calm Jack Dorsey now has two full-time jobs: executive chairman of Twitter and CEO of Square, his new service that lets anybody accept credit-card payments with their iPhones. It's a good thing he believes in magic. "From a product standpoint," he says, referring to Square, "we want every touch point to feel magical. It inspires trust." It starts with data. Before Twitter and Square, Dorsey developed dispatch software that tracked ambulances and taxis, revealing urban design f laws that suggested new ways to streamline city services. Square speaks to the relationship between a buyer and a seller, which can be similarly studied and streamlined. "Payments are a form of communication that could be better designed, less burdensome," he says. "What customized information could be on a receipt? We can do that." Dorsey sees the data that Square can provide as an opportunity to give artists, small-business owners, and vendors new insights. With knowledge comes better inventory control, smarter customer-retention strategies, growth, jobs, and happy communities. But it starts with the product. "It's about leading by design."