  This paper discusses challenges and design strategies in responsive design
for thematic maps in information visualization. Thematic maps pose a number of
unique challenges for responsiveness, such as inflexible aspect ratios that do
not easily adapt to varying screen dimensions, or densely clustered visual
elements in urban areas becoming illegible at smaller scales. However, design
guidance on how to best address these issues is currently lacking. We conducted
design sessions with eight professional designers and developers of web-based
thematic maps for information visualization. Participants were asked to
redesign a given map for various screen sizes and aspect ratios and to describe
their reasoning for when and how they adapted the design. We report general
observations of practitioners' motivations, decision-making processes, and
personal design frameworks. We then derive seven challenges commonly
encountered in responsive maps, and 17 strategies to address them, such as
repositioning elements, segmenting the map, or using alternative
visualizations. We compile these challenges and strategies into an illustrated
cheat sheet targeted at anyone designing or learning to design responsive maps.
The cheat sheet is available online:
https://responsive-vis.github.io/map-cheat-sheet
