Plot became spatial in some 20th-century attempts to understand and schematize narrative structure. In writing manuals and journals, diagrammers charted major plot points, connecting branches of subplots, and graphing interactions between people and objects in time. Some diagrams were aids for authors needing to organize complicated plots in, for example, a mystery novel. Such visualizations were particularly helpful for writers of long series, ensuring a mix of continuity of relationships and originality in plot points.