interprete bubble plot and plotting negative numbers in ggplot2
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I asked a question about making bubble charts in ggplot2 [here][1] [http://stackoverflow.com/questions/11517411/ggplot2-how-to-manually-adjust-scale-area]

My follow-up question is how do I interprete the scale_size in the legend?  

Does small dot (labeled 10) mean the data can be anything from 5-10?  If the data for a particular point is 8, does scale_area function change the data point to 10 before it is presented as a dot size 10 on the graph.

Also is there a way to plot negative number on ggplot bubble chart?  Some software can make the negative data a color bubble.   