One of the most time-consuming and labor-intensive steps in map production involves the delineation of cartographic and cultural features such as lakes, rivers, roads, and drainages in aerial photographs. These features are usually traced manually on a digitizing table in painstaking detail. This paper investigates an alternative approach, an interactive graphically designates a feature of interest by pointing at or crudely tracing it with a display cursor. Using this input as a guide, the system employs context-dependent, scene-analysis techniques to extract a detailed outline of the feature. The results are displayed so that errors can be corrected by further interaction, for example, by tracing small sections of the boundary in detail. This interactive approach appears applicable to many other problem domains involving large quantities of graphic or pictorial data, which are difficult to extract in digital form by either strictly manual or strictly automatic means.