Clusters and the Cosmic Web
  We discuss the intimate relationship between the filamentary features and the rare dense compact cluster nodes in this network, via the large scale tidal field going along with them, following the cosmic web theory developed Bond et al. The Megaparsec scale tidal shear pattern is responsible for the contraction of matter into filaments, and its link with the cluster locations can be understood through the implied quadrupolar mass distribution in which the clusters are to be found at the sites of the overdense patches. We present a new technique for tracing the cosmic web, identifying planar walls, elongated filaments and cluster nodes in the galaxy distribution. This will allow the practical exploitation of the concept of the cosmic web towards identifying and tracing the locations of the gaseous WHIM. These methods, the Delaunay Tessellation Field Estimator (DTFE) and the Morphology Multiscale Filter (MMF) find their basis in computational geometry and visualization. 
Rien van de Weygaert (1) ((1) Kapteyn Institute, University of   Groningen, the Netherlands)