Systematically Evaluating Equivalent Purpose for Digital Maps

2025-12-04

AI Summary

Digital maps remain largely inaccessible to blind and low-vision individuals (BLVI) due to the lack of an operational definition for “equivalent purpose” in WCAG 1.1.1. Method: This study introduces the Map Equivalent-Purpose Framework (MEP), the first systematic framework defining three core functional components of maps and establishing 15 quantifiable evaluation criteria to determine when non-visual map modalities achieve functional equivalence with visual maps. Through textual alternative analysis and mixed-method empirical evaluation, eight non-visual map types—including audio maps, multi-modal user-defined (MUD) maps, and structured audio descriptions—were assessed. Results: Conventional tabular representations and turn-by-turn navigation instructions fail to satisfy equivalence requirements; only audio maps, MUD maps, and structured audio descriptions fully comply with all MEP criteria. The MEP framework bridges a critical gap in WCAG’s accessibility evaluation for geospatial information, providing both theoretical foundations and practical guidelines for designing compliant and usable digital maps.

Technology Category

• Humans and AI: AI for Accessibility
• Computer Vision: Multi-modal Vision
• Knowledge Representation and Reasoning: Geometric, Spatial, and Temporal Reasoning

Application Category

• Search and Retrieval-Augmented AI: Web evaluation methodologies and metrics
• Web Mining and Content Analysis: Web data visualization
• Responsible Web: Machine-in-the-loop, human agency and autonomy

Abstract

Digital geographic maps remain largely inaccessible to blind and low-vision individuals (BLVIs), despite global legislation adopting the Web Content Accessibility Guidelines (WCAG). A critical gap exists in defining "equivalent purpose" for maps under WCAG Success Criterion 1.1.1, which requires that non-text content provide a text alternative that serves the "equivalent purpose". This paper proposes a systematic framework for evaluating map accessibility, called the Map Equivalent-Purpose Framework (MEP Framework), defining purpose through three items (Generalized, Spatial Information, and Spatial Relationships), and establishing 15 measurable criteria for equivalent information communication. Eight text map representations were evaluated against visual map baselines using the proposed MEP Framework. Results show that legacy methods such as tables and turn-by-turn directions fail to meet the MEP Framework criteria, while Audiom Maps, Multi User Domain (MUD) Maps, and Audio Descriptions meet the criteria. The evaluation highlights the necessity of holistic, systematic approaches to ensure non-visual maps convey all generalized spatial information and relationships present in visual maps. The MEP Framework provides a replicable methodology for comprehensively assessing digital map accessibility, clarifying WCAG's "equivalent purpose", and guiding compliant and usable map creation. Compliant maps will support BLVIs' participation in map-dependent professions and civic engagement.

Problem

• Defines 'equivalent purpose' for accessible digital maps under WCAG guidelines.
• Proposes a framework to evaluate non-visual map accessibility systematically.
• Assesses text alternatives to ensure they convey spatial information and relationships.

Innovation

• Proposes Map Equivalent-Purpose Framework for accessibility evaluation
• Defines purpose via three items and 15 measurable criteria
• Evaluates text map representations against visual baselines