WHAT
The data-ink ratio pattern relates to the amount of ink used to provide useful information. It compares the amount of data versus the amount of ink, or pixels, used in the display. A well-designed app should aim for a high ratio of relevant to irrelevant information, or a high ratio of data to ink. The goal is to increase the ink used to communicate signal and reduce content that contributes to noise. Following this rule will improve the efficiency of the map in communicating necessary information.
WHY
At a time when big data is omnipresent, it becomes more important to edit and curate the content and its visualization. The American statistician Edward Tufte uses the term data – ink ratio to argue against using excessive decoration in visual displays and calls superfluous information “chart chunk.” Tufte states that an effective graph should aim to maximize the data-ink ratio, which represents the ratio of relevant to irrelevant information. For a well-designed map, this means that a large share of the pixels should present useful information.
WHEN
As a basic rule, apply the data – ink ratio to any map that is part of an app. Pay special attention to single-purpose apps (see chapter 6) that are designed for people with less GIS experience and little time and patience to work through their task. These apps require that the map and the UI components are built with minimum distraction and chart chunk. Data – ink ratio is also vital for maps on mobile devices that have limited space to paint needed information. Any noise on a small screen will severely decrease usability.
HOW
Always strive to show what is important while simultaneously removing what is not important. Start by asking, “What is the minimum set of visuals necessary to communicate the information understandably?” and continue by asking, “Which elements, such as layers, features, labels, or ornaments, can be removed without degrading the essence that needs to be communicated?”
Increase the amount of pertinent data points and decrease unnecessary content. The following techniques help increase the data-ink ratio:
- Basemap layer: Choose simple basemap layers such as light gray, dark
gray, or human geography by default. Use basemap toggle to change the
basemap layer to a visually more challenging option such as Imagery. - Operational layers: Remove or hide layers that aren’t necessary. Use layer
list or theme toggle to make selected layers visible. Simplify features and
apply scale dependency that hides layers when they are not needed at a
certain scale. - Labels: Be selective and show labels only when they help the reader,
apply scale dependency, and decrease label density. Prefer sans serif fonts
over serif fonts. - Cartography: Follow cartographic rules such as reduced color choices and
strong contrast.
Another common problem related to the data – ink ratio is the display of noncontinuous geographies. Noncontinuous geographies are areas that are spread apart — for instance, the US states of Alaska and Hawaii are geographically dispersed from the continental states. As shown in figure 7.5, showing all 50 states at the same time would also require displaying Canada, which uses most of the ink but isn’t relevant in the context of the US-centric map. Use the following solutions to work around the problem of noncontinuous geographies:
- Placemarks: Use shortcuts to predefined places such as smaller territories
to avoid showing widely dispersed data. - Inset maps: Use multiple views to move dispersed geographies closer to
each other.
EXAMPLE
A common problem in apps that show data for the US is that the states of Alaska and Hawaii, as well as US territories, are widely dispersed. Builders must make the difficult decision to default the map extent on the continental 48 states or show all. Showing all states and territories will decrease the data-ink ratio, whereas the former fails to be inclusive. The app in figure 7.6 uses inset maps to display Alaska, Hawaii, and the Virgin Islands close to the continental states. Each inset view makes intelligent use of local map projections to preserve area and shape. Pop-ups are moved out of the small view window and attached to the main app. Because Alaska is a large state, it is important to let users navigate its view. On the contrary, there isn’t much value in zooming or panning the views of Hawaii and the Virgin Islands, so their navigation is disabled. Inset maps are difficult to display on mobile devices, so the app removes them on small-screen resolutions.
continental states, Alaska, Hawaii, and the Virgin Islands.
MORE EXAMPLES
Canada is not relevant to the US-centric map but still uses most of the ‘ink’
REFERENCES
[1] The Visual Display of Quantitative Information; Tufte, E.; 1983; https://www.edwardtufte.com/tufte/books_vdqi (accessible: 11/4/2020)
[2] Signal-to-Noise Ratio; Chen, X.; September 9, 2018; https://www.nngroup.com/articles/signal-noise-ratio/ (accessible: 11/4/2020)