WHAT
Comparing changes, patterns or differences in data is difficult to impossible with interactive controls on a single map view.
WHY
Small Multiples is sometimes also called trellis maps or tile maps. It is a series of similar maps using the same size and scale, allowing them to be easily compared.
Our brain is great at perceiving simple visual features like color, shape or size. Small Multiples allow the human eye to jump back and forth between similar maps for which the brain will instantly compare differences. Users only need to learn to understand one map and can then apply this knowledge to the rest of the maps which shifts their attention to the patterns and meaning of the data.
Small Multiples add context to a view without making the user do additional work through interactive controls, it is therefore often a better cognitive choice than a time slider.
WHEN
Use to find patterns of change in the data and compare measures across multiple maps in one concise view. One way to structure small multiples is to use a sequence of maps to show progression over time, e.g. population change over the last 100 years. Another form is to create a multi-dimensional grid the compares a domain (e.g. race) across their values (e.g. Whites, Blacks, Hispanics, Asians, Other) along their income.
HOW
Create a grid of postage-stamp sized maps that are indexed by category or label and sequenced over time or ordered by a quantitative variable. Each individual map should share the same measure, scale, size, and shape to show a different slice of the data for each map.
Simplicity is critical part of small-sized maps. Reduce the number of data points to less than 30, e.g. states (polygons) or observations (points). Displaying the maps in logical order like geography, variable, or time will help users to quickly find the map they are interested in and see variations to the neighboring maps.
Consider making maps interactive to provide additional details or clickable to select the current version for display in full screen.
EXAMPLES
