This volume is an array of demographic data which can often be pictured in an intelligible and graphically striking way by a shaded contour map. The data might pertain to population levels or to rates of fertility, marriage, divorce, migration, morbidity, or mortality. Most often the data are structured by age and time-e.g., age-specific death rates over time.
Shaded contour maps permit visualization of such demographic surfaces and offer a panoramic view impossible to obtain from the usual graphs of levels or rates at selected ages over time or a selected times over age. Contour maps are particularly effective in highlighting patterns in the interaction of age, period, and cohort effects.
This monograph presents a bouquet of shaded contour maps to suggest the broad potential of their use in population studies. The value of such maps lies in their substantive import. Graphic designs, E.R. Tufte concluded, should give “visual access to the subtle and difficult, that is, the revelation of the complex”. Demographic surfaces can be particularly complex. A mortality surface, for example, might be defined over a century of age and a century of time, comprising 10,000 date points that may vary over four orders of magnitude. Shaded contour maps are an arresting, efficient, and clear means of giving demographers visual access to such data.
William Playfair, the pioneer of graphic methods for presenting statistical data, argued that with a good visual display “as much information may be obtained in five minutes as would require whole days to imprint on the memory, in a lasting manner, by a table of figures”. The 100 shaded contour maps in this monograph summarize more than a half million data points in a memorable, revealing manner.