Presenting node-link structures with modification

A sequence of steps presents node-link representations on a display. The sequence includes a first step, a last step, and at least one intermediate step. The first step presents a first representation that represents a first node-link structure. The last step presents a last representation that represents a second node-link structure that is a modified version of the first node-link structure. Both node-link structures include a set of shared elements that include a moving element. The moving element is represented by features that have different positions in the first and last representations. Each intermediate step presents an intermediate representation that includes features representing a subset of the shared elements including the moving element, and each element in the subset is also represented by features in the first and last representations. The feature representing the moving element has object constancy through the sequence of steps. The modification can include both deletion and insertion, and the sequence can include a first subsequence in which features are deleted and a second subsequence in which features are inserted. Moving elements can follow paths that are not parallel straight lines. Separate changes can be concurrently animated.