Design principles for origin-destination flow maps

ABSTRACT

Origin-destination flow maps are often difficult to read due to overlapping flows. Cartographers have developed design principles in manual cartography for origin-destination flow maps to reduce overlaps and increase readability. These design principles are identified and documented using a quantitative content analysis of 97 geographic origin-destination flow maps without branching or merging flows. The effectiveness of selected design principles is verified in a user study with 215 participants. Findings show that (a) curved flows are more effective than straight flows, (b) arrows indicate direction more effectively than tapered line widths, and (c) flows between nodes are more effective than flows between areas. These findings, combined with results from user studies in graph drawing, conclude that effective and efficient origin-destination flow maps should be designed according to the following design principles: overlaps between flows are minimized; symmetric flows are preferred to asymmetric flows; longer flows are curved more than shorter or peripheral flows; acute angles between crossing flows are avoided; sharp bends in flow lines are avoided; flows do not pass under unconnected nodes; flows are radially distributed around nodes; flow direction is indicated with arrowheads; and flow width is scaled with represented quantity.

KEYWORDS:

• Origin-destination flow maps
• movement mapping
• graph drawing
• cartographic design principles
• aesthetic criteria
• map design

Acknowledgments

The authors thank Tanya Buckingham (UW Madison), Juliane Cron (TU Munich), Ken Field (Esri Inc.), Daniel Huffman (UW Madison), Charles Preppernau (National Geographic), Hans van der Maarel (Red Geographics), and Tim Wallace (New York Times) for providing flow maps for the content analysis. The authors also thank the study participants.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1. We observe that longer flows are curved more than shorter flows or peripheral flows on maps used for the quantitative content analysis, but have not analyzed the effectiveness with a user study.

Additional information

Funding

This work was supported by the U.S. National Science Foundation (NSF) [Grant number 1438417].