Rural people tend to adopt regular linkages with particular trade centres. Trade areas are the zones over which they regularly travel to towns and cities for goods and services. The trade areas map is based on a postal sample survey of 2000 randomly-selected rural households located outside towns of 200 or more people, and conducted in 1982-83 by the Department of Geography, University of Adelaide. The intricate patterns depict the very complex task of supplying the scattered rural population with a great variety of goods and services

Country Towns

Apart from a few almost empty areas and areas directly served by major cities, this level of trade area covers all the settled districts. It brings the majority of rural householders within reach of basic services such as primary and secondary schools, weekly shopping facilities, and general practitioner and local government services. In some areas there is slight overlap between the trade areas of neighbouring towns.

The size of the circle is proportional to the volume of retail and selected service sales in 1979-80 Census of Retail and Selected Service Establishments conducted by the Australian Bureau of Statistics. Where two or more towns fall within the one statistical collection area the sales have been apportioned according to the number and types of shops or services. Although retail sales symbols are shown for small centres, data are insufficient to define trade areas. Some of the small centres, such as Port Wakefield, Hawker and Robe, derive substantial sales from passing traffic or tourism, while others such as Iron Knob and Wallaroo are special function towns without significant rural service populations.

Most country towns providing ordinary shopping needs recorded turnover values between $1 million and $10 million, but some of the largest, such as Clare, Millicent and Naracoorte, had values between $20 million and $30 million.

The average distance between towns varies greatly over the State. One of the reasons is the variation in rural population density shown by the green shading. Even the settled districts have few places where there are more than two persons per square kilometre (excluding residents in towns of 200 or more people), while vast areas of the outback have densities of less than one person per 10 square kilometres.

Two opposing forces influence the spacing of country towns. On the one hand, the householder's desire to keep travel time and costs to a minimum would create many closely spaced towns. On the other hand, the desire of business firms to maximise their total volume of sales would require large trade areas and fewer widely spaced centres. Each commercial establishment must be able to reach enough customers to keep it in business. Where population density falls too low for businesses to reach sufficient purchasing power, the network of trade centres thins and disappears as in much of the inland pastoral area.

Since the Second World War personal mobility has increased and the real cost of travel has fallen. Many of the smallest towns have lost some or all of their trade-centre functions, while the medium and larger sized towns have consolidated their position. On Eyre Peninsula the low population densities require large trade areas in order to produce turnover volumes sufficient to keep the widely spaced service centres viable. On Fleurieu Peninsula, by contrast, where population density is much higher, equal or higher turnovers are derived from much smaller trade areas, despite the loss of much trade to Adelaide.

Other factors which affect the spacing and sales volumes of country towns include variations in the level of rural income, the degree of competition for business presented by major service centres, especially Adelaide, and historical influences. The core area of the State from Adelaide to Quorn was mainly settled by 1890 and has inherited what is now an excessive number of towns, mostly with small trade areas and low levels of sales. A typical example of the influence of these factors is the Riverton district in the Mid North, which may be compared with the more recently settled area near Cleve on eastern Eyre Peninsula.
Regional Service Centres

The nine major regional service centres are distinguished by substantially larger trade areas which are superimposed over, and may completely overlap, the trade areas of one or more of the smaller towns. These centres supply the more specialised goods and services which are not available in smaller towns. Regional service centres also compete with the smaller towns to some extent by supplying standard goods and services, such as supermarket goods. The growth of even large regional service centres in South Australia has been impeded because particular activities have been divided among several towns within the same district. Thus steel-making, power generation, base-metal smelting, and the repair and maintenance facilities for Australian National railways are divided between the three towns of the Iron Triangle-Whyalla, Port Augusta and Port Pirie. In the past the copper mining, copper smelting, seaport and rural service functions of upper Yorke Peninsula were shared between the Cooper Triangle towns of Kadina, Wallaroo and Moonta. In the Riverland irrigation areas Renmark, Berri and Loxton share regional service roles as do Nuriootpa, Tanunda and Angaston in the Barossa Valley.

The trade areas of the major regional service centres do not entirely cover the settled districts. Kangaroo Island, for example, has direct links with Adelaide for higher-level services. Mount Gambier loses little trade to Adelaide. Its sales volume compares closely with metropolitan local government areas with large shopping centres, such as Glenelg or Elizabeth. Port Lincoln, with less than half the sales volume of Mount Gambier, however, extends its trade area over most of Eyre Peninsula.
Adelaide

The high concentration of population and purchasing power in Australian capital cities gives them overwhelming dominance in service activities. Thus, the City of Adelaide (excluding the suburbs) in 1979-80 recorded a turnover of $756.3 million compared with $111.3 million for the largest country centre, Mount Gambier. Adelaide casts a 'trade shadow' over the whole State, drawing off some spending which might otherwise take place in country towns and regional service centres. The inset map of Adelaide's trade shadow depicts the percentage of specialised household expenditure estimated to be outlaid in Adelaide by respondents to the rural household sample survey in 1982-83.

Adelaide's impact is heavy in its immediate vicinity, throughout the Mid North, and on Yorke Peninsula. These areas nevertheless have a sufficient density of population to support a closely spaced system of country towns. A study of five small towns in the Mid North in 1980 showed that between 20% and 50% of locally earned income passed through local service centres, with a heavy 'leakage' of trade flowing to nearby larger towns such as Clare and Gawler, or to Adelaide and its northern suburbs.

Adelaide tends to fill the vacuum wherever population density is low or alternative shopping facilities are limited. Thus, the upper South-East makes very intensive use of Adelaide as, to a lesser degree, does the sparsely peopled inland pastoral zone. Here, remote stations may use light aircraft, mail orders and occasional major shopping trips to obtain goods from Adelaide. Conversely, near major service centres such as Port Lincoln, Adelaide's role in supplying the rural population of falls to low levels.