Map Design

Design Variety

5710.2 - Origin-destination flow maps

Wednesday, July 5
4:30 PM - 4:50 PM
Location: Coolidge

Origin-destination flow maps show the quantity and direction of movement between start and end points. Design principles for origin-destination flow maps are largely based on expert intuition and tradition rather than scientific evidence. Automated methods for creating origin-destination flow maps do not take design principles into account, resulting in maps with overlapping flows that are difficult to read. We identify common design principles for origin-destination flow maps and develop an automated method to create flow maps.

Content Analysis for the Identification of Design Principles
We conducted a content analysis with 97 origin-destination flow maps without branching or merging flows to identify design principles used by cartographers. We found that line width is used almost exclusively to show different quantities; sharp bends in flow lines are avoided; the number of intersections of flows is minimized; and arrowheads are the only means used to indicate flow direction (Jenny et al., submitted-a).

User Study to Evaluate Selected Design Principles
We conducted an online user study with 215 participants to evaluate select cartographic design principles for origin-destination flow maps. Results show that curved flows are often easier to read than straight flows; arrows indicate direction more effectively than tapered line widths; and flows between circular start and end symbols are easier to read than flows between areas (Jenny et al., submitted-a).

Automated Creation of Origin-destination Flow Maps
We developed a force-directed layout method for creating origin-destination flow maps that takes into account the design principles identified in the content analysis and the user study (Jenny et al., submitted-b). The developed method reduces overlaps among flows and avoids sharp or irregular bends in flow lines. We conducted a survey of professional cartographers and found that the automated flow maps are similar in quality to manually produced flow maps.

A Web Map for Visualizing a Large Origin-destination Movement Dataset
We ported the automated method for creating origin-destination flow maps to JavaScript to create an interactive migration map of the United States. The map shows state-to-state and county-to-county migration. Migration flows between distant counties are aggregated per state. States are shown as nodes with a circular arrangement around the map to reduce clutter and the amount of interaction required to view flows (Stephen and Jenny, submitted).

Conclusion
We identify and evaluate design principles to guide cartographers designing flow maps. We also introduce a force-based creation method for non-branching origin-destination flow maps. The automated method is fast enough for creating interactive web maps on-the-fly, and the resulting automated flow maps are similar in quality to manually produced flow maps.

Acknowledgement
This work was supported by grant 1438417 from the U.S. National Science Foundation (NSF).

References
Jenny, B., Stephen, D. M., Muehlenhaus, I., Marston, B. E., Sharma, R., Zhang, E., Jenny, H. (submitted-a). Design principles for origin-destination flow maps. Cartography and Geographic Information Science.
Jenny, B., Stephen, D. M., Muehlenhaus, I., Marston, B. E., Sharma, R., Zhang, E., Jenny, H. (submitted-b). Force-directed layout of origin-destination flow maps. International Journal of Geographical Information Science.
Stephen, D. M. and Jenny, B. (submitted). Automated layout of origin-destination flows: U.S. County-to-county migration 2009-2013. Journal of Maps.

Bernhard Jenny

Associate Professor
Monash University

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Daniel M. Stephen

Geography
Oregon State University

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Brooke E. Marston

Cartographer
U.S. Department of State

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Ian A. Muehlenhaus

Department of Geography, University of Wisconsin, Madison

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Kenneth Field

Resident Cartographer
Esri Inc

Dr Kenneth Field is a self-confessed cartonerd. After 20 years in UK academia he now works at Esri in cartographic research and development. He undertakes research, writes, teaches and blogs about map design, is Past-Editor of The Cartographic Journal, co-founder of the Journal of Maps and is on the advisory board of the International Journal of Cartography. He is Chair of the ICA Map Design Commission, Fellow of the British Cartographic Society and Royal Geographic Society and a Chartered Geographer (GIS). He has won numerous awards for mapping and for cartographic pedagogy. He tweets as @kennethfield and blogs at cartonerd.com.

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