Bubble Chart:

• A Bubble Chart is a multi-variable graph that resembles a combination of a Scatter plot and a proportional area chart
• Where X and Y axis are separate variables
• However unlike a Scatter Plot, each point is assigned a label or category
• Colours can also be used to distinguish between categories or used to represent an additional data variable.
•  Time can be shown either by having it as variable on one of the axis or by animating the data variables changing over time.
• Bubble Charts are typically used to compare and show therelationships between labeled/categorised circles, by the use of positioning and proportions. The overall picture of Bubble Charts can be use to analyse forpatterns/correlations.

This is the Bubble chart between the GDP and CO2 Per capita

http://www.datavizcatalogue.com/methods/bubble_chart.html#.U_DyacWSyd0