Over the years, many a quick'n'easy method has been developed for determining the economic vitality of a city, methods that don't rely so much on crunching numbers as they do on quick observations. They are not meant for precision, merely a broader accuracy. The Economist, for example, created the Big Mac index back in the 80's, using the theory that you could tell how inflated an economy is by the relative price of a Big Mac.
Another popular one, more popular than most due to its ease of use, is The "Crane" Index, which operates on the theory that the number of visible cranes in the sky line is directly related to the economic activity and consumer confidence of a given city. I took this picture of a part of Xi'an's skyline yesterday afternoon.
Xi'an's doing alright by that system of measure, I'd say.