Four pieces of information are contained within this single graph: Human Development Index, Population, Population Density, and city climate (tropical, arid, temperate, snow). In the original image this was likely printed in color, which would enhance understanding significantly. This kind of graph makes it easy to group cities and quickly understand what kind of features are shared among groups of cities. Due to the large number of cities in the left top of this graph, it is hard to see the relationships in this particular graph. However, less cluttered graphs that presented fewer cities were included in this same publication and made for easier understanding.