Resource management and conservation require the definition of planning units (PUs), i.e., the spatial domain where management decisions are applied. PUs are either pre-established in size and shape following management constraints or are data driven(DDPUs) by overlay of multidisciplinary data layers. The trade-offs between these two approaches have not been investigated previously for small tropical islands and their characteristics. Here, we use resource density, fishing pressure and susceptibility to mortality for a giant clam fishery in a small French Polynesia atoll to discuss the suitability and impact of the two approaches in conservation management. Aggregation to pre-established PU grids highly affected data even for PU as small as 2500 m(2), with higher loss of spatial information for density and fishing effort. By contrast, DDPU rendered well small scale patterns of interest but reduced redundancy. Our results stress the importance of considering the initial patterns of data in the definition of planning units, and we suggest a 3 steps process to identify adequate trade-offs between PU size, PU redundancy and data loss to properly draw practical recommendations for small islands. (C) 2015 Elsevier Ltd. All rights reserved.