An information retrieval system in which a set of distinct information items map to respective nodes in an array of nodes by mutual similarity of the information items, so that similar information items map to nodes at similar positions in the array of nodes comprises: a graphical user interface for displaying a representation of at least some of the nodes as a two-dimensional display array of display points within a display area on a user display; a user control for defining a two-dimensional region of the display area; and a detector for detecting those display points lying within the two-dimensional region of the display area; the graphical user interface also displaying a list of data representing information items, being those information items mapped onto nodes corresponding to display points displayed within the two-dimensional region of the display area.