From CS 294-10 Visualization Sp10
This visualization is an attempt to show the disparity between the total amount of funding and the funding per person from each country. Some countries, such as the United States and Japan, have high total aid, but relatively low aid per person. Other countries, such as Guyana, Estonia, and Luxembourg, have pledged a small amount of aid in total, but their pledge is a large amount per person. This visualization also divides the world into three groups ("Americas", "Europe", "Asia, Africa, & Australia", and "Other"), inviting comparisons between the groups. The total amount of aid pledged by the "Other" group is shown below the nations, but is aligned to invite comparison between the government and non-government entities.
The nominal variable Group (e.g., "Americas") is encoded by color. The nominal variable Organization (e.g., "United States" and "Private") is encoded by vertical position. The vertical position of each Organization also encodes the ordinal relationship between the total amounts pledged. The quantitative variable Pledged Amounts (both total and per-person) is redundantly encoded by the length of the bars and the horizontal position of the end of the bar. Finally, the quantitative variable Population is implicitly encoded by the relationship between the bars on the left and the bars on the right; however, this is a weak encoding of population and is hard to read off the charts.
To allow the viewer to estimate the quantities shown, vertical grid lines are shown. The lines are light gray to emphasize the data. To invite comparisons between the total and per-person amounts, the bar charts are aligned vertically so that one Organization label refers to both. The color coding scheme only uses four categories, because Asia, Africa, and Australia are small groups by themselves. If each continent were encoded by color separately, there would be too many colors, resulting in a "busy" appearance. A light gray box is drawn around the legend to indicate that it is not another bar chart.
As mentioned by other students, the amount given per person does not take into account the relative prosperity of that nation. Introducing other variables, such as the per capita GDP, might help normalize the data shown. (I admit that I know very little about economics, so GDP may not be the best indicator of prosperity. It's just a suggestion.) Changing the x-axes to logarithmic scaling would allow easier comparison between the very short bars; however, ratios between the bar lengths would become less meaningful. The population of each nation is "hidden" in the ratio between the total amounts and the per-person amounts pledged. The Population variable could possibly be explicitly encoded with another encoding.