"Planning is centrally concerned with land-use and related environmental, social and economic activities within a legislative, administrative and political context. Its distinctive approach lies in integration and co-ordination both of policy development and its implementation, by statutory and other means. It is a process for assisting the public, private and voluntary sectors in making choices about land-uses and related decisions for the conservation and development of land and its resources, in ways conducive to sustaining the natural, economic and social environment of Australia."
A definition from the Planning Institute of Australia; http://www.planning.org.au/careers/edu_policy.ssi

Planning is a dynamic activity that impinges on many aspects of everyday life in metropolitan and rural areas. Planning as a general term can mean an activity that seeks to provide an alternative to uncoordinated and ad hoc decision-making. For cities, suburbs and regions, planning targets the development, improvement, conservation and general management of the environment. There are in fact many specialist plannings: land use, social, transport, regional, and so on. The BPlan degree touches on many of these aspects.

The scale of urban planning ranges widely: from small local precincts through town and regional centers to specialized land use and environmental zones up to metropolitan areas and wider regions. The actual nature of planning also varies: detailed site planning and design; ensuring development proposals comply with environmental and community standards; documentation and evaluation of emergent urban problems and issues; broader-brush strategic work defining desirable future outcomes; policy analysis and implementation.

There are also therefore several different settings in which planning is carried out: state government departments and authorities, local councils, development companies, planning consultant firms, and voluntary and special-interest organizations.

These different roles do not always mesh seamlessly and mediation, the reconciliation of opposing viewpoints, and the management of conflict are important planning tasks alongside research and data analysis; predicting, guiding and controlling development; communication; and plan and policy formulation. Urban planning issues are invariably multidimensional and usually political. They can encompass many different types of processes and consequences: physical, economic, social and aesthetic. Planners are routinely called upon to integrate and coordinate inputs from a wide array of legitimate stakeholders to ensure efficient, equitable and environmentally sustainable outputs.

Planning impacts on the way people live, work, and play. It helps shape what, where, when, and how development should occur. It seeks to be a force for improving the quality of life. Urban planners thus make a vital contribution in determining how cities, suburbs, towns and rural areas change over time.