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The development of community and regional planning policy, when done well, is an exercise in the rational application of knowledge (information and relationships) to the determination of just, equitable, appropriate, economically efficient, and politically effective public actions.
Rational planning assumes the availability of data upon which to make decisions. But in the early 1900s, when the first large-scale modern city plans were created, such data simply did not exist. It was not until 1907 that the Russell Sage Foundation undertook the first statistical survey of an American city in Pittsburgh. National housing statistics were not available until the 1940 Census was reported, and reliable data on traffic generation by land use type did not appear until the 1980s.
Given this general lack of dependable information, most planning focused on gathering local population statistics; mapping land use data, and traffic patterns and volumes; and mathematically projecting this information into the future to arrive at bases for a physical plan to accommodate these projected future "needs."
What might be termed the "classic" planning process, as developed in the early decades of the 20th century, followed three sequential steps: (1) data gathering; (2) plan making; and (3) plan implementation.
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