I study cities. Last year, I visited 57 of them while logging almost 200,000 miles. This year, I’ve already made four trips to Nashville and will make second trips to Indianapolis and Kansas City shortly. Why do I keep going back to these cities? While they aren’t the usual economic powerhouses — like New York, San Francisco, Los Angeles and Washington — they are the next in line, with surging economic growth and impressive revitalization. In a world where talent and yield are scarce, these secondary cities are increasingly popular among investors. In a survey by the real estate services company CBRE this year, for example, Orlando outranked New York in appeal by real estate investors.