than 10,000 GW-ton-yr, distortion in the energy spectrum, thus statistics, will dominate the sensitivity [@huber2002]. Such exposure corresponds to about 8 years for Daya Bay. Therefore, for most cases, the rate deficit will dominate the sensitivity, and related systematic uncertainties, including the detection efficiency, target proton number, and backgrounds, should be controlled to $\lesssim 0.5$% to measure $\sin^22\theta_{13}$ to 0.01 at 90% confidence level.

When multiple reactor cores are spread out over a large area, a single near site can only constrain the antineutrino flux from the nearby cores. In this case, the reactor-related uncertainties cannot be completely cancelled by the near-far relative measurement. Moving the near site farther away from the cores will improve the cancellation but lose sensitivity due to an increase in the oscillation effect. To obtain the best sensitivity, Daya Bay is configured with one far site for observing the maximal oscillation effect, and two near sites for determining the flux of the reactor antineutrinos from the Daya Bay and Ling Ao NPPs. The best locations of the three halls were determined with a $\chi^2$ method [@sunyx], with the projected uncertainties and estimated background at the candidate sites derived from geological survey information. For the optimal 