Graduated Symbol Maps

Instead of representing quantity with color intensity, these maps use symbols (typically bubbles) to depict quantity (via the sizes of the bubbles), and these bubbles are centered at corresponding locations.

Some advantages:

• size is a better indicator of quantity than color intensity

• the perception of the value represented by area isn't influenced by region size (this is because color perception is affected by size, so maps like choropleth maps unknowingly give more importance to larger regions)

• symbol maps also make it possible to visualize more than one attribute (by allowing us to use more than one channel); for example, size can be used to represent a quantitative attribute, while color hue can be used to represent a categorical attribute in the same map

  

  Here, the color hue represents the party while the bubble sizes represent the number of votes