Researchers are aware that a majority of the CpG islands are unmethylated. How to represent this fact in a graphic?
The above picture created with ggplot2 explains us how the CpG methylation across the CpG Islands is distributed for each chromosome. Each CpG island is shown as a single dot(.). Methylation on the CpG island is identified by the color gradient. This explains that most of the CpG Islands are unmethylated (overlapped dots are seen as a line on the left side of the picture). Sparsely methylated CpG Islands can be identified as blue dots on the right side. Click the picture for a larger view.