How similar are fish and fibre? What about oil and aircraft? How would you even answer the question? From the perspective of productive knowledge, these questions do have answers, arising principally from the revealed common knowledge required to produce one or another product. Here, we show how Hidalgo & Hausmann go from the what of trade across countries to make inferences about just this. And, produce one of the more eye-catching data visualisations of the decade: the product-space.