Glossary

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Perceptual Congruence(also: Perceptually Congruent Structure)

A design principle for accessible representations that requires the structure of a non-visual interface (such as a screen reader navigation tree) to mirror the visual structure of the original graphical representation. A perceptually congruent screen reader structure preserves…

Personal Data Externalization(also: Data Externalization)

The process of representing internal experiences — thoughts, emotions, behaviours, bodily states — in some external medium such as a drawing, written word list, spreadsheet, physical artefact, or tracking log. Drawing on Larkin and Simon's distinction between internal and…

Pitch Mapping(also: Pitch-Y Mapping, Frequency Mapping)

A sonification technique that maps data values to auditory pitch, where higher values produce higher-pitched sounds and lower values produce lower-pitched sounds. In accessibility contexts, pitch mapping is commonly used to represent the vertical position (Y-axis) of data points…

Reference Sonification(also: Audio reference tone, Origin tone)

A sonification design pattern in which a fixed, recognisable audio tone represents a known landmark - typically the origin of a coordinate system or another anchor point - and can be re-played on demand so that a user exploring a non-visual data space can re-orient themselves…

Relational Diagram(also: Relational Information Display, RID)

A graphical representation that depicts items (nodes) and the relationships (links) between them using a two-dimensional spatial layout. Common forms include entity-relationship diagrams, flowcharts, state diagrams, network diagrams, and mind maps. Relational diagrams encode…

Relief Chart(also: 3D Chart, Haptic Chart, Relief Graph)

A tactile data visualization that uses height (the third dimension) to encode data values, making charts accessible to people with visual impairments through touch. Unlike flat tactile graphics that use only texture or raised lines, relief charts represent data magnitude through…

Scalable Vector Graphics(also: SVG)

An XML-based vector image format for two-dimensional graphics that supports interactivity and animation. Unlike bitmap formats (JPEG, PNG, GIF) which store images as grids of pixels, SVG describes shapes, paths, and text mathematically, allowing images to scale without loss of…

Semantic Level(also: Semantic Content Level, Alt Text Semantic Level)

A framework for categorizing the depth of information conveyed in alt text descriptions of data visualizations, introduced by Lundgard and Satyanarayan. The four levels are: Level 1 (construction details such as chart type, axes, and encodings), Level 2 (statistical properties…

Small Multiples

A series of similar graphics or charts arranged in a grid or sequence, each showing a different frame, condition, or time point, used to illustrate change or comparison. In tactile graphics, small multiples are the traditional method of representing movement or temporal change —…

Statistical Graph(also: Statistical Chart, Data Graph, Quantitative Graph)

A visual representation of numerical or statistical data using geometric elements such as lines, bars, points, or areas to convey patterns, trends, relationships, and comparisons. Common types include line graphs (showing trends over time), bar charts (comparing categories), pie…

Tactile Graphic Reader(also: Tactile Graphic Display, Tactile Image Reader)

A device that combines physical tactile graphics (raised-line images on paper) with digital audio feedback, enabling blind and visually impaired users to explore graphical content through touch while receiving spoken or sonified information about the elements they contact.…

Thematic Map(also: Statistical map)

A map designed to communicate a specific theme or statistical variable across a geographic region — population density, income, election results, climate, disease prevalence — rather than to depict general topography or physical features. Thematic maps include choropleth maps…

VLAT(also: Visualization Literacy Assessment Test)

A standardized 53-item test developed by Lee, Kim, and Kwon to measure a person's ability to read and interpret data visualizations across 12 chart types. Widely used as a baseline for comparing visualization literacy between groups and for evaluating the impact of assistive…

Verbosity Level(also: Verbosity Setting, Detail Level)

A configurable setting that controls the amount of detail provided in text or audio descriptions of content, particularly for screen reader users and accessible data visualizations. Verbosity levels typically range from low (minimal summary with key points only) to high…

Vibro-Audio(also: Vibrotactile Audio, Vibro-Tactile)

Vibro-audio is a multimodal interaction technique that combines vibration feedback from a device's built-in motor with auditory cues to convey information non-visually. On touchscreen devices, vibro-audio enables users to explore graphical content through touch — the device…

Visual Data Exploration(also: VDE, data visualization exploration)

Visual data exploration is the interactive process of examining datasets through graphical representations such as charts, maps, and dashboards to discover patterns, trends, and anomalies. Accessibility considerations are critical because conventional visualizations rely…

Visualization Literacy(also: Data Visualization Literacy, Graphical Literacy, Graph Literacy)

The ability to read, interpret, and extract meaningful insights from visual data representations such as charts, graphs, maps, and infographics. Visualization literacy encompasses skills like identifying trends, making comparisons, understanding scales and axes, and critically…

Visualization Question Answering(also: Chart QA, Visualization QA, VisQA)

A class of interactive systems that let users ask natural-language questions about a data visualization — a chart, graph, or map — and receive direct textual or spoken answers rather than having to interpret the visualization themselves. Visualization QA systems typically…

VoxLens

An open-source JavaScript plug-in developed at the University of Washington that improves the accessibility of online data visualizations for screen-reader users through a multimodal approach. VoxLens provides three interaction modes: a Question-and-Answer mode where users can…