The study illustrates, through the use of three approaches, a methodology for identifying the spatial structure of temporal trends in birth rates within the census divisions (counties) of Québec. Mapping of birth rates based upon the standard deviation is difficult because the latter masks certain of the trends which are identifiable for the period 1926-1971. A second method, that of allometry, cannot be used directly, but the notion of the relation between the demographic behaviour of each county and that of Québec does allow for the development of a third method, i.e., the relative growth, by period, of county birth rates compared to that of Québec as a whole. The curve illustrating the evolution of Quebec's birth rate can be broken down into five periods, each of which manifests different temporal trends. These periods serve as a basis for analysis of each individual county. Regression analysis then permits the calculation of a rate of growth at the county level which is then divided by the growth rate of the province to yield an index of relative change. Mapping of these indices reveals a period of waning birth rates from 1926-1937, an upswing from 1937 to 1947, a period of stability from 1947 to 1957, and the beginning of a decline from 1957 to 1964. Finally, a period of exceptionnal decline can be observed from 1964 onward. Each of the maps thus reveals the spatial variations of each of the preceding trends.