106 TerraCost addresses the problem of computing multiple-source weighted least-cost-path surfaces for grid terrains. Currently, this functionality is provided by the GRASS module r.cost. Our approach, implemented in GRASS as r.terracost, expands this functionality such as to allow massive terrains to be processed efficiently. We obtain this efficiency by combine memory- and disk-based techniques, and, as a by-product of the algorithm's modular design, we can actually benefit from cluster-connected computing resources (if available). Experiments show that TerraCost’s algorithms perform well in practice: Our implementation outperforms standard solutions as dataset size increases relative to available memory and our distributed solver obtains near-linear speedup when preprocessing large terrains for iterated computations with varying parameters. FOSS4G2006 - Free And Open Source Software for Geoinformatics Session 3 : GRASS Desktop Laura Toma ltoma@bowdoin.edu Thomas Hazel Jan Vahrenhold Rajiv Wickremesinghe Laura Toma ltoma@bowdoin.edu <MaKaC.conference.ContributionType object at 0xb3c094ac> GRASS