# Enhancing Color Scales for Active Data Physicalizations
## 3 Related Works  
A literature review was conducted to identify how colors are applied in data physicalizations, what type of data these colors encode, whether there are related evaluations, and the number of color values used, among other issues.  
Articles published in the repositories of ACM, IEEE, Wiley Online, and Springer were selected, in the period between 01/2005 and 01/2023, with the following keywords: \"data physicalization\", \"data visualization\", \"data materialization\", \"tangible data\", \"tangible data\", and \"active\". The repository query returned 1016 results.  
Both the inclusion and exclusion processes were conducted by two evaluators with experience in information visualization and data physicalization. The main rule for including an article in the final review selection is that the color applied in the data physicalization should encode abstract data, regardless of the number of color values applied. Another criterion used was that the physicalization of data, which must be aimed at coding and communicating data, be a complete article, and be written in English. The article exclusion criteria considered non-complete articles, articles outside the scope of this research, duplicate articles, and articles that did not contain any of the research keywords in their title, abstract, or keywords.  
Thus, 25 articles were selected, with a time interval between 2014 and 2023: 22 from ACM, 2 from the WILEY, and 1 from IEEE. Table 2 contains the final selection of the articles.  
The articles selected for analysis were read in full to extract information and categorize the following data: Data Physicalization Type; External Actuators; Dynamic Color (Hue, Saturation, Brightness); Color Palete; InfoVis Techniques; Color Evaluation; DataDimensions; Color Values.  
The analysis of the articles showed that 36% of physicalizations are dynamic, 40% are rearrangeable, 16% are passive, and 8% use more than one type. Furthermore, 52% of physicalizations do not use any external actuator, compared with 40% that use some type, and 8% use it in a hybrid way. Regarding color, 64% of inspections use dynamic colors, 36% use static colors, and only 20% of the total allow you to configure hue, saturation, or brightness. The types of color palette uses characterized in these articles were 64% categorical, 12% sequential, and 28% using both palettes. There are no references to the use of a divergent color palette.  
Figure 3: Application of the Farnsworth-Munsell test (**a**); Polar Chart showing the total number of errors in the ordering test (**b**). Section (**a**) is allowed under CC BY-SA 4.0 Deed, 2019, Image and License, Section (**b**) is adapted, allowed under CC BY-SA 4.0 Deed, 2021 [33]. We focused on the chart.  
Regarding InfoVis techniques, 87% present a single technique, 44% use a bar chart, 12% use scatter plots, 4% use pie charts, and 24% use other types. It is worth mentioning that the vast majority of the articles, around 88%, did not present a color evaluation for data physicalizations. Regarding the data dimensions mapped in data physicalization, 36% map one dimension, 28% map two dimensions, 32% map three dimensions, and 4% map more than three data dimensions. The color values used to encode the data are 1D-- 16%-1D, 2D--12%, 4D--12%, 5D--32%, 6D--12%, and +6D--6%.  
The analysis also presented other relationships, such as a trend toward using active physicalizations compared with passive ones in more recent years, which use external actuators in their design (67%). In this context, the colors can then allow for the configuration of hue, saturation, and brightness and use more than one type of color palette.  
Considering only active data physicalization, just 11% conducted a color evaluation, 44.5% mapped three data dimensions, 66.6% used six or more color values, 66.6% used more than one color palette, and 33.3% allowed hue, saturation, and brightness to be configured to the map data. No automated evaluation procedures for the colors in data physicalization were found.