Number (default: 50)
In the force-directed layout this setting defines the optimal length between 2 nodes, which directly correlates to the state of the link between them. If a link is longer than there will be a force pulling the nodes together, if the link is shorter the force will push the nodes apart. The optimal length is more and indication in the algorithm than a guarantee that all nodes will be at this distance. The result of the layout is really a combination of the incidence structure of the diagram, the initial topology (positions of the nodes) and the number of iterations.
In the layered layout it defines the minimum distance between nodes on the same level. Due to the nature of the algorithm this distance will only be respected if the the whole crossing of links and optimization does not induce a shift of the siblings.
This setting is specific to the force-directed layout and layered layout