International competitions and John Harrison’s 18th-century invention of a marine chronometer accurate enough for a ship to determine its transitory longitude at sea inspired a host of technological improvements to the chronometer that enabled wider applications of chronometers to 19th-century astronomical problems: notably to cartography and to data recording. From the 1820s through the 1840s, European and American astronomers collaborated on major international chronometric expeditions, transporting dozens of marine chronometers between fixed and temporary astronomical observatories to determine accurate longitude differences between land masses and to improve the precision of interior maps. The widespread commercial adoption of the telegraph in the 1840s and 1850s enabled longitudes to be further refined over long overland or transoceanic distances. Both chronometric and telegraphic techniques became important through the 19th century in systematically mapping the American west. They serendipitously led to the discovery of the finite speed of an electromagnetic signal through telegraph wires. Moreover, they revolutionized the efficiency of transit instrument and meridian circle observations of stellar positions for star catalogues, becoming standard astronomical data-recording techniques within the walls of an individual observatory.