1. A system to generate a layered visualization of a software system, the system comprising: a storage device to store a model of a software system, the model defining a plurality of entities of the software system and relationships among the entities; at least one processor; and a visualization tool executable on the at least one processor to: generate nodes representing the entities of the software system model; assign the generated nodes to layers in a set of ordered layers in accordance with rules associated with the layers to generate a layered layout, including the layers, of the software system, wherein the assigning includes evaluating, for a given one of the nodes, the rules and determining that the given node satisfies a particular one of the rules, the given node being assigned to the layer associated with the particular rule; render an interactive visualization of the layered layout for display; receive importance levels for respective ones of the nodes, wherein at least two of the importance levels are different; and group at least some of the nodes into a group node in the interactive visualization according to the importance levels of the nodes.