This paper explores the relationship between physical population and population changes. The 1st section examines the objectives of physical planning the tools that are available to pursue the objectives and the main constraints on its effectiveness. A 2nd section explores the relationships between population projections and physical planning including illustrations from Sydney and emphasizing the significance of many dimensions of physical change for physical planning. Planning is the making of decisions in light of expected future circumstances as well as current circumstances. The term "land use planning" offers a good clue to the nature of physical planning. Planning the use of land means planning the location of the various uses of land in relation to one another: houses roads factories shops parks schools and even underground services such as water and sewer mains and telephone lines. Physical planning is less concerned with ensuring that the correct quantities of each of these facilities are provided than that they are provided in appropriate places in relation to one another. Physical planning seeks very broad objectives through the control over land use. These include: protection of the amenity of an area from changes in land use which though they might be in the interests of a single property owner are not necessarily in the interest of others living working traveling or taking recreation in the vicinity; coordination of the provision of the various private and public elements in urban development so that services and facilities are available where required and when needed; ensuring that private developments occur in places that can be readily provided with public services at an acceptable cost; and ameliorating some of the inequities between individuals and groups that can follow from the operation of the property market and from the segregation of social and economic groups which it often produces. As well as land use planners individuals responsible for planning of services and infrastructure need projections of populations within small areas. When planning is defined as the making of decisions in the light of the expected future as well as the current situation it can usefully be classified into 2 different levels. The first facility planning involves the planning of individual facilities or services or a single class of such facilities. Such planning is based on estimates of future demand or need for the facility in each locality which in turn is based in part on population projections. The second coordinative planning aims to ensure that the different elements of a city -- housing shopping services employment opportunities transport facilities -- are provided in the best location in relation to one another. Land use planning is concerned about the composition and the activities of the population as well as the simple numbers of people who live in each locality. Some examples illustrate the richness and diversity of the relationships between planning and demographic analysis in local areas.