  The Cherenkov Telescope Array (CTA) is the major next-generation observatory
for ground-based very-high-energy gamma-ray astronomy. It will improve the
sensitivity of current ground-based instruments by a factor of five to twenty,
depending on the energy, greatly improving both their angular and energy
resolutions over four decades in energy (from 20 GeV to 300 TeV). This
achievement will be possible by using tens of imaging Cherenkov telescopes of
three successive sizes. They will be arranged into two arrays, one per
hemisphere, located on the La Palma island (Spain) and in Paranal (Chile). We
present here the optimised and final telescope arrays for both CTA sites, as
well as their foreseen performance, resulting from the analysis of three
different large-scale Monte Carlo productions.
