By 2027, half the U.S. population will be freelance. If cities focus on that, attracting independent workers and startups suddenly seems a lot more important than, say, courting Amazon. Last year, 238 cities across North America submitted themselves to Amazon as the hopeful site of its next headquarters, spurred by the promise of 50,000 high-paying jobs and $5 billion in investment. In January, the tech giant narrowed that pool down…