Spatial Diffusion of Disease - Instructional Web Server -疾病空间扩散教学Web服务器—.pptVIP

Spatial Diffusion of Disease Diffuse is defined as ‘to disperse or be dispersed from a centre; to spread widely, disseminate’. (Oxford English Dictionary) In the geography, the term diffusion, has distinct usages: Expansion diffusion Relocation diffusion Combined expansion and relocation diffusion Expansion diffusion Expansion diffusion: the process whereby a phenomenon of interest (this may be information, a material artefact, a disease), spreads from one place to another. In this expansion process, the item being diffused remains, and often intensifies, in the originating region, but new areas are also occupied by the item in subsequent time periods. t1, t2, t3 denotes time 1, 2 and 3 respectively Relocation Diffusion Relocation diffusion: is a spatial spread process, but the items being diffused leave the areas where they originated as they move to new areas. Combined Expansion and Relocation Diffusion The diagram below how the two processes of expansion and relocation may be combined. Types of Spatial Diffusion An Example of a Combined Diffusion Wave Types of Expansion Diffusion Expansion diffusion occurs in two ways. Contagious spread Hierarchical spread Cascade diffusion Contagious spread Contagious spread depends on direct contact. This process is strongly influenced by distance because nearby individuals or regions have a much higher probability of contact than remote individuals or regions. Therefore, contagious spread tends to occur in a centrifugal manner from the source region outward. Hierarchical spread Hierarchical spread involves transmission through an ordered sequence of classes or places, for example from large metropolitan centres to remote villages. For example, within socially structured populations, innovations may be adopted first on the upper level of the social hierarchy and then trickle down to the lower levels. Cascade diffusion is a term reserved for processes that are always assumed to be downwards from lar