The masses of 64 short-lived neutron-deficient nuclides covering the element range from tungsten to uranium have been obtained for the first time. They have been evaluated by combining directly measured masses from Schottky mass spectrometry with linked experimental Q-values in α-decay chains. Based on these new mass data we have determined the one-proton and two-proton drip-lines as well as the size of the "littoral shallow" of the sea of instability. No evidence of a Thomas-Ehrman shift has been found in the region of the investigated heavy nuclides. A peculiar behavior of two-proton separation energies has been observed in the lead region. The predictive power of various mass models is investigated.