SPANmirror

Spanmirror is a visualization technique and accompanying software component designed to represent collections of time-based intervals, or spans, in a mirrored two-dimensional layout. In the usual arrangement, each span is defined by a start time and an end time and is assigned to a category, track, or layer. A central axis serves as a mirror line; the start position is plotted on one side of the axis and the end position on the opposite side, producing a symmetric silhouette that highlights interval overlap, containment, and gaps.

The layout supports multiple spans across categories, enabling comparison of patterns across groups. Spans may be displayed as arcs, ribbons, or line segments, with color, opacity, and height encoding additional attributes such as source, weight, or confidence. The algorithm handles nesting by stacking spans on each track and can optionally compress or expand time scales to reveal macro- or micro-structure. It can also generate summary statistics on overlaps and coverage.

Spanmirror is used in fields such as event log analysis, scheduling optimization, genomic interval analysis, and performance profiling. It complements traditional timelines and heatmaps by emphasizing symmetry and overlap relationships that are less obvious in linear layouts.

Variants include symmetric mapping, where the axis is centered and time values are mirrored, and antisymmetric mappings for directed intervals. Limitations include potential visual clutter with large numbers of spans and the need for careful color and layout choices to preserve readability.

See also: timeline visualization, interval arithmetic, interval tree, chord diagram.