For decades, the Peace Research Institute Oslo has analyzed customs data for weapons across the globe, figuring out which countries are buying and selling small arms, light weapons like portable artillery systems, and ammunition. This information is available online, but Google recently took the hard numbers and turned them into an interactive map that tells you just where weapons are going and how much countries are spending. The chart is divided by imports and exports as well as military or civilian classes, which refer to the type of weapon (i.e. revolvers and sporting rifles are civilian, assault rifles and machine pistols are military) rather than who it's being sold to. Google and the Igarape Institute — which also helped build the system — explain the tool and some major data gaps in this PDF, but the system itself is both easy to understand and fascinating.