Visualizing Change in Thematic Maps: Influence of Spatial Discretization and Interactive Comparison Modes on Usability

Map comparison is a fundamental step to geographic inquiry, enabling users to detect spatiotemporal changes and identify spatial correlations. Several comparative layouts exist, but their effectiveness is limited by visual change blindness and data presentation formats. This study examines the interplay between two comparative layouts (i.e. side-by-side juxtaposition and slider-based transition) and spatial discretization geometries (hexagonal and square grids, and irregular administrative polygons) over three levels of complexity. We conducted a user experiment with 39 participants (N = 344 trials) logging response times and error rates. Results show that slider-based transition significantly improves efficiency in high-complexity visual search tasks. However, performance varied across task complexity: side-by-side juxtaposition showed better accuracy in low-complexity tasks. Spatial discretization geometry has acted as an essential mediator: hexagonal grids outperformed irregular polygons both in response time and error reduction. Hence, comparative layout efficacy cannot be evaluated in isolation, but is bound to the underlying spatial aggregation geometry.