The Darling Downs district embraces 7,000 square miles and contains eighty-three central places, with populations ranging approximately from 10 to 50,000. It has the most extensive occurrence of medium to high density rural settlement in Queensland.
Prominent differences in hierarchical status between groups of central places are identified in relation to four variables: population size, central service workforce size, the variety of central functions, and the number of business telephones installed. Five hierarchical classes are recognized: hamlet, village, small town, large town and small city. The clearest separation of the settlement array into discrete groups is revealed graphically by comparing centres in terms of the relationship between workforce size and the number of business telephone stations installed.
For each group of central places, employed persons account for about one-third of the total population. For villages and higher order classes of settlement, the most prominent field of employment, attracting about one-third of the workforce, is that comprising commercial, financial, and personal service activities. In hamlets, as a group, more employed persons are engaged in agriculture and farm contract work than in any other major occupational class. In general, in successively higher order groups of central places along with a reduction in the prominence of the agricultural workforce there are increases in the proportions of female employment, and of those engaged in manufacturing, building/construction and maintenance, and professional service. Retirement normally assumes a greater importance in places of higher centrality status.
The regional service relations of Downs centres are examined in an extensive area comprising the Darling Downs district and its neighbourhood. Together they embrace approximately 42,000 square miles in southern Queensland and northernmost New South Wales.
For each settlement, the spatial analysis of its external service relations is made with reference to a number of representative central services which varies according to the centre's status: small city (32), large town (24), small town (16), village (8), and hamlet (4). For each settlement group, the services selected include those surveyed for lower order centres.
For each central place, in respect of each service activity examined, a surrounding service-area is delimited. A general conformance in outline of a majority of the service-areas of individual centres is revealed. The degree of correspondence is assessed in terms of service range variability.
The composite of all service-areas surrounding a central place is divided into three (inner, intermediate and outer) zones characterized by relatively strong, appreciable and relatively weak attraction.
The combined area of a central place's inner and intermediate zones of service attraction is regarded as constituting its urban field or complementary region. It embraces all localities which are included in at least one-quarter of the service-areas delimited for a centre.
Increases in the hierarchical status of central places are accompanied by increases in the population size of their urban fields. At the time of survey (1961) the estimated population of Toowoomba's urban field was 27,780. The average values for lower order groups of settlements were: 10,326 (large towns), 2,375 (small towns), 475 (villages), and 118 (hamlets).
The expectations of Christaller's theories regarding the shape and size of complementary regions and the location of their boundaries in relation to subordinate centres are markedly at variance with field evidence. The urban fields of Downs centres are generally elongated in form. Their configuration does not approximate that of any regular geometric figure.
In general, urban fields of centres of similar status
(a) resemble one another more closely in population size than in area;
(b) are separate in location or overlap only to a minor extent; and
(c) are not consistently 'nested' within those of centres of the next higher order.
A comparison of the urban fields of successively higher order settlement classes reveals that an increase in centrality is accompanied by
(a) an extension of the average and extreme range of service attraction,
(b) a reduction in the margin by which rural dwellers outnumber central place residents, and
(c) a lowering of the ratio between the populations of the urban field and its centre. Only the highest order centre, Toowoomba, has a population which is larger than that of its complementary region.
In general, the locations of equal gravitational force (as predicted by Reilly's model relating to retail trade) correspond closely with the 'breaking-points' in overall service dominance between centres of small town, large town, and small city status.
For each small town and higher order place, the urban field delineated is broadly congruent in outline and population size with the centre's combined region of service dominance and subdominance.