Lecture 4 - Spatial Diffusion Pattern Analysis Five general...

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Spatial Diffusion & Pattern Analysis
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Five general types of spatial diffusion processes… 1. Expansion Diffusion – a simple outward expansion from the source (covering a larger, more extensive area over time). 1 2 3
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2. Relocation Diffusion – the movement and displacement of something away from its origin (across space) over time. Study area
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3. Contagion Diffusion – the outward movement or spread of something from a point of origin, with variable intensity (as related to the likelihood of localized interaction, contact, or exposure due to proximity) and a pronounced distance-decay.
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Such knowledge can be used to model or estimate outbreaks over time w.r.t. a source location.
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4. Hierarchical Diffusion – the diffusion down a hierarchy of places (typically from large to medium-sized places, and then on to smaller places over time); from core to peripheral or hinterland areas.
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5. Mixed Diffusion Processes – any combination of the diffusion processes 1 through 4 (occurring simultaneously or overlapping in space… and enhanced by site and situational factors). time (t) t=1 t=2 t=3 diffusion
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Note that any combination (or all) of these processes may be influencing a point pattern or distribution… making modeling a difficult task. Nevertheless, the distribution of point density counts per unit area (i.e., the frequency counts of the number of points by quadrats or cells) is something that can be analyzed numerically using various theoretical probability distributions. Once a best-fit distribution is found or a process is identified, it can be used to model the point pattern, and/or be used to the variability in the spacing of points or point density over space and time.
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Mapping the incidence of a given phenomenon over space to provided a descriptive analysis of a pattern (be it a point pattern or areal trend) is important not only as a visual tool that can accentuate a spatial analysis, but also as technique that can help one gain insights as to the processes that might be responsible for generating a spatial pattern. The study of spatial patterns has been of extreme interest to those in spatial epidemiology.
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Books that are must reads for those interested in analyzing the spread of disease and statistical methods useful in monitoring its diffusion.
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Whatever the underlying process, spatial patterns that are generated by spatial processes many times end up being systematic or “spatially dependent”… i.e., spatially auto-correlated . The most common form being “positive” spatial autocorrelation--where “like” values tend to cluster in space. Consider the following spatial patterns as good examples of positive spatial dependence…
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Eastern Equine Encephalitis 2009 (Jan. 1 – October 6, 2009): 249 cases
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Spatial Incidence of Heartworm 2005
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Rabies Cases (2005)
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Swine-Flu cases Fall 2009
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Spatial Distribution of West Nile Virus cases 2007 ..contagion process?
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This note was uploaded on 02/15/2012 for the course GEO 6938 taught by Professor Staff during the Summer '08 term at University of Florida.

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Lecture 4 - Spatial Diffusion Pattern Analysis Five general...

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