Trends in Patterns Versus Patterns in Trends: A Key Distinction for Visualizing Geographic Time-Series Data

We typically conceptualize patterns in geographic time series in one of two ways: as trends in spatial patterns or as spatial patterns in trends. Chronological map serieseither animations or small multiples of chronologically-sequenced mapshave become a standard approach to mapping geographic time series. I propose that this approach is generally effective for visualizing trends in patterns but not for visualizing patterns in trends. On the other hand, trend summary maps (e.g., change maps, time-series glyph maps, trend cluster maps, and trend component maps) are generally effective for visualizing patterns in trends but not trends in patterns. Trend summary map techniques deserve more attention because they can help us identify and illustrate spatio-temporal patterns in ways that chronological map series cannot.