  A precise measurement of the cross section for the process e+e- -->
K+K-(gamma) from threshold to an energy of 5 GeV is obtained with the
initial-state radiation (ISR) method using 232 fb^{-1} of data collected with
the BaBar detector at e+e- center-of-mass energies near 10.6 GeV. The
measurement uses the effective ISR luminosity determined from the e+e- -->
mu+mu-(gamma)gamma_ISR process with the same data set. The corresponding
lowest-order contribution to the hadronic vacuum polarization term in the muon
magnetic anomaly is found to be a_mu^{KK, LO}=(22.93 +- 0.18_{stat} +-
0.22_{syst}) * 10^{-10}. The charged kaon form factor is extracted and compared
to previous results. Its magnitude at large energy significantly exceeds the
asymptotic QCD prediction, while the measured slope is consistent with the
prediction.
