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Finding the quickest route from A to B can be tough if you’re new in town. But instead of messing about with a bit of string and a map, Darwin Reyes at Imperial College in London and colleagues at Harvard University turned to gases to point the way. They etched a map of London streets onto a 4 by 5-centimetre sliver of glass and covered it with another flat sheet of glass. They then pumped helium into the channels formed by the streets. Electrodes were used to mark a starting point and a destination. When a voltage was placed across the two electrodes, the electric field found the shortest path between the electrodes and made the helium glow like a fluorescent tube (Lab on a Chip, vol 1, p 113). Reyes demonstrated the glass chip’s route-finding capability by making it light up the shortest route between Imperial College in Kensington, west London, and Big Ben.