Ages, chemical compositions, velocity vectors, and Galactic orbits for stars in the solar neighbourhood are fundamental test data for models of Galactic evolution. We aim to improve the accuracy of the Geneva-Copenhagen Survey data by implementing the recent revision of the Hipparcos parallaxes. The new parallaxes yield improved astrometric distances for 12,506 stars in the GCS. We also check the GCS II scales of T_eff and [Fe/H] and find no need for change. Introducing the new distances, we recompute M_V for 16,086 stars, and U, V, W, and Galactic orbital parameters for the 13,520 stars that also have radial-velocity measurements. We also recompute stellar ages from the Padova stellar evolution models used in GCS I-II, using the new values of M_V, and compare them with ages from the Yale-Yonsei and Victoria-Regina models. Finally, we compare the observed age-velocity relation in W with three simulated disk heating scenarios to show the potential of the data. With these revisions, the basic data for the GCS stars should now be as reliable as is possible with existing techniques. Further improvement must await consolidation of the T_eff scale from angular diameters and fluxes, and the Gaia trigonometric parallaxes. We discuss the conditions for improving computed stellar ages from new input data, and for distinguishing different disk heating scenarios from data sets of the size and precision of the GCS.
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