Yes, they are one-line drawings, but they are also much more. Dr. Bob Bosch, a mathematician who teaches at Oberlin, created this image of Botticelli's Birth of Venus using the shortest possible line while still rendering the image. It's an illustration of the Travelling Salesman Problem.
What's that? The Oxford Dictionary of Psychology defines it as:
The problem of finding the shortest path that passes through a set of given points once and only once, as when a travelling salesman needs to visit a number of specified cities exactly once, using the shortest possible route. The problem is notoriously difficult to solve, because the number of possible tours rises rapidly with the number of cities.
You can see five other examples here, including images of the Mona Lisa and a Van Gogh self-portrait.
-via Flowing Data