As computers get smaller every day, cities are getting smarter. If you can slap a sensor on anything–which at this point, costs pennies–you can track it. And cities are discovering a hunger for big data: Navigant Research forecasts that smart city technology investment will reach $27.5 billion by 2023. Odds are your city has already bought into the trend. Here are eight cities changing their urban fabric with sensors, crowd sourcing and all things big data.