In architect Michael Arad‘s vision for the memorial, the names were to be laid according to where people were and who they were with when they died – not alphabetical, nor placed in a grid. Inscribed in bronze parapets, almost three thousand names would stream seamlessly around the memorial pools. Underneath this river of names, though, an arrangement would provide a meaningful framework; one which allows the names of family and friends to exist together. Victims would be linked through what Arad terms ‘meaningful adjacencies’ – connections that would reflect friendships, family bonds, and acts of heroism. through these connections, the memorial becomes a permanent embodiment of not only the many individual victims, but also of the relationships that were part of their lives before those tragic events.

Over several years, staff at the 9/11 Memorial Foundation undertook the painstaking process of collecting adjacency requests from the next of kin of the victims, creating a massive database of requested linkages. Often, several requests were made for each victim. There were more than one thousand adjacency requests in total, a complicated system of connections that all had to be addressed in the final arrangement. In mathematical terms, finding a layout that satisfied as many of these adjacency requests as possible is an optimization problem – a problem of finding the best solution among a myriad of possible ones. To solve this problem and to produce a layout that would give the Memorial Designers a structure to base their final arrangement of the names upon, we built a software tool in two parts: First, an arrangement algorithm that optimized this adjacency problem to find the best possible solution. And second, an interactive tool that allowed for human adjustment of the computer-generated layout.