1. A method comprising: obtaining node-link data defining a node-link structure; the node-link structure including nodes and links, each link relating at least two of the nodes; and using the node-link data to present a sequence of representations of the node-link structure on a display, the display having an edge along one side acting as a horizon; the sequence beginning with a first representation and ending with a last representation; the last representation being perceptible as a changed continuation of the first representation; each representation in the sequence including bounded node features representing nodes in the node-link structure; each bounded node feature having a position and a region around the position; the regions around the positions of the bounded node features in each representation together determining a first convex hull for the representation, each representation's first convex hull enclosing a total area for the representation; the bounded node features of each representation including a subset of more spaced node features, the regions around the positions of the more spaced node features determining a second convex hull for the representation, each representation's second convex hull enclosing a sufficient portion of the representation's total area to serve as a focus on the nodes within the second convex hull, and enclosing a region in which bounded node features have nearest node spacings along an axis prependicular on the display to the horizon, that are in general perceptibly greater than in a region enclosed by the first convex hull but outside the second convex hull; the nodes represented in at least one on the first and second representations forming at least one peripheral branch, each peripheral branch including a top level and at least one lower level, the top level including a top level node and the lower levels including lower level nodes that are not in the representation's subset of more spaced node features, each node at each lower level having a parent node at a next higher level to which the node is related through one link; lower level node features that share a parent node feature having centers of area positioned on the display in order approximately along a line generally parallel with the horizon with sufficiently similar spacings along the axis perpendicular to the horizon from the region around the parent node feature and with sufficiently similar spacings in a dimension generally parallel to said horizon from adjacent node features along the line that the lower level node features sharing the parent node feature are perceptible as a group of related node features; the second convex hulls of the first and last representations including subsets of bounded node features that represent different sets of nodes; the sequence of representations producing a perception that at least one bounded node feature has a nearest node spacing that increases from the first representation to the last representation and that at least one other bounded node feature has a nearest node spacing that decreases from the first representation to the last representation.