Spatial Patterns: Flows and Barriers/ Les traces spatiales: flux et barrières Jean-Pierre BOCQUET-APPEL 108 SPATIAL ANALYSIS OF BIODEMOGRAPHIC DATA

Spatial patterns of variables can exhibit in many forms: areas of continuous, clinal, wavy or erratic changes, areas of homogeneity se-parated by zones of rapid changes. This characterization is not inde-pendent on the level of geographic aggregation of the factor scale on which the biodemographic data are sampled (Briggs, 1992). A change perceived as random at a local scale may be clinal at a continental one, and conversely. Among these surface reliefs, the zones exhibiting a major discontinuity, an abrupt change of the values taken by the variable(s) are particularly interesting. They generally delineate pat-terns and probably correspond to the zones of sharp changes for the causal variable(s) underlying the observed surface relief or to barriers in dynamic processes. An example of this, in demography, can be two contiguous areas of mortality generated by ecological and/or socio-economic factors. A rapid change of the factors on the map, corres-ponds to a sharp change of the mortality (Bocquet-Appel, 1993)