Abstract
Some of the geographic information is best presented by flow maps, for instance, the exhibition of the interactions among places or regions. Current commercial graphics software do not provide any ready-to-use function for drawing "flow map". Although a few programs for drawing flow maps have been developed in the past, they are developed under different software environments, and the design of the flow lines are not suitable for presenting some of the geographic interactions. Based on the topology built by ARC/INFO computer software, the authors use the C language to calculate the directions and widths of flow lines demonstrating the spatial interactions among patients and medical institutes. This study aims to exhibit regional patients-to-clinics or patients-to-hospitals trip patterns. Arrow-headed straight lines with varied widths are used to indicate the trip direction from patients' residence to hospitals and the magnitude of the flow. Since some of the patients receive their treatments locally, a background choropleth maps of varying shadings are used to provide this information. Questionnaires are designed and used to test the readability of the maps drawn by this program. It is concluded that the maps effectively express regional patterns of trips among patients and medical institutes.