Visiting a friend? It's only polite to bring a little something with you.
Heads of state aren't exempt from this unspoken rule, except that every present the White House accepts from other foreign dignitaries must be logged, tagged, and stored in official archives. (For the unfamiliar, there's an excellent "West Wing" episode about this.) Gift-giving is a routine part of diplomacy, but it also makes for interesting public data.
On Thursday, President Obama released a list of all the gifts he accepted in 2011 on behalf of the United States. For each gift, the PDF names the donor country, a description of the gift, an estimate of its value and a reason why Obama accepted it (typically something having to do with not wanting to make a scene by rejecting the present, even if they were just boring old "Witcher 2" DVDs). Faced with all this government data, there was only one thing to do with it: plug everything into a spreadsheet and see which foreign leaders outspent each other to impress the most powerful man in the world. The heat map above ranks countries according to the total value of their 2011 gifts to Obama, with darker colors representing more generous states.