How not to do data visualization

I was glancing over Hacker News and came across an article from the Economist Daily Chart blog.  The daily chart was about nations debt management.  The following can be shown here.

Seems innocent enough.  It shows in declining order the debt per nation.  What a second?  Why is Ireland have more debt than USA? After reading the article more thoroughly it looks like it is a percentage of GDP.  What a third time?  Is the bar graph the percentage of GDP or the number in the white box a percentage of GDP?  And how does this relate to debt management?  So apparently in the article it explains the change in primary balance for each nation to be 60% of GDP.  So the bar graph is a % change of GDP to get to 60% of GDP.  Are we crystal?  I'm not sure I totally understand but that is my basic understanding.

Data visualization is important in Analytics and Operations Research.  We need to model real world applications quite a lot.  Often times there is no better way to do this than to use a chart or graph.  The real art is conveying the crux of the message to the recipient.  There is an internet meme devoted to the art of bad chart making.  I feel bad using the Economist as an example because after all I did finally (I think) come away with the right idea.  But still notice how there are no data or axis labels across the top of the chart.  Also the numbers in the white boxes are not given any units.  I'm still not sure if those numbers in the white box are a percentage or a debt value.  Sometimes the visual art clutters the real message.  It is important to make sure that recipient has the right frame of reference and can understand each graphic and label.