For example, polygon can be drawn to emphasize the contour of certain areas so that audience's attention can be led to certain areas; legend, made by the annotation of text and symbols, can be added to wherever you want in the map and with format that are not in standard SAS legend templates; images can be overlaid with transparent background so that the map is not obscured by the background the of image. Results: These SAS macros for mapping VDW data have the advantages of creating highly customized maps by reusable code without extra cost of specialized mapping software or training.
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Chimmula et al. (2012) studied this question.