Tim,
Poor quality maps, both topographical and nautical, plagued the Allies throughout the campaigns in the Pacific. There is at least one account of the crew of a U.S. sub (U.S.S. Wahoo I think) used an elementary school geography textbook to locate and naviagte the appraoches to Wewak, New Guinea. The Marines on Guadalcanal were issued topo maps that were totally inaccurate. MArines resorted to drawing their own maps. It would be safe to assume that the topo maps of Niku, which were from the same, or earlier time period, would have been equally inaccurate.