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In section Symbolization you will find 2 references to an image that is not there. The mentioned source Roth, Robert E. "Dot Density Maps." also does not include this. In the PDF it just says "FIGURE 1 HERE". This section sounds like somebody just copied it from somewhere and forgot the images. Where does this come from? 18.104.22.168 (talk) 08:23, 13 May 2011 (UTC)