A sound economic base is essential for cities. Historically, their economic foundations have been diverse, ranging from heavy industry in places like Berlin to seats of government as in Vienna. The base can change: cities may find new sources of growth as previous ones wither – tourism, for example, in many of today’s older cities.
One way or another, economic strength is necessary: it attracts populations and gives them economic opportunities; it generates the income that supports a wide range of secondary activity; and it provides the tax base to fund collective infrastructure and public services. And size seems to matter. There is considerable evidence of the cumulative effects of urban growth.