The Time-Gun Map of Edinburgh, published in 1861, overlays concentric circles to show “the time taken for the sound of the one o’clock gun to travel from Edinburgh Castle to different parts of Edinburgh and Leith.” Being able to calculate that your neighbourhood is eight seconds away, say, from the one o’clock signal and being able to set your clock that precisely — well, David Tomlinson would be elated. Via Kottke.