The sixth volume of the Transactions on Computational Science journal contains the thoroughly refereed best papers selected from the International Conference on Computational Science and Its Applications, ICCSA 2008. All 21 papers included in the issue have been significantly revised and extended following the event. The journal has been divided into two parts. The 11 papers in Part 1 are devoted to the theme of information systems and communications and the 10 papers in Part 2 focus on geographical analysis and geometric modeling.