From interoperability to interpretability: distilling design indicators to support maritime spatial planning data representation in Europe

This study investigates how cartographic design influences the communicative effectiveness of Maritime Spatial Planning (MSP) geoportals in Europe. While data interoperability has advanced under the MSP and INSPIRE Directives, communication interoperability remains inconsistent, limiting cross-border comprehension and stakeholder engagement. Drawing on graphic semiology and contemporary digital cartography, the paper develops a design-based analytical framework combining semiological, cognitive, and interactive indicators to assess four MSP platforms: Italy's Portale del M semantic metadata linkage, Denmark's Havplan.dk, Finland's MSP 2030, and the EMODnet MSP Geoviewer. The comparative analysis reveals that interactivity, perceptual balance, and semantic coherence strongly influence usability and interpretability, whereas inconsistent colour semantics and static interfaces hinder understanding. The study suggests that technical harmonisation alone is insufficient: visual design can be understood as a structuring component of how MSP information is communicated within governance processes. Accordingly, the paper proposes a Design-Driven Harmonisation Framework structured around seven principles: semiological consistency, perceptual colour uniformity, interactive transparency, hierarchical legibility, semantic metadata linkage, accessibility, and visual narrative coherence and illustrates their operationalisation through a conceptual exercise applied to four MSP layers. By embedding design considerations within MSP data infrastructure, this framework offers a complementary pathway towards geoportals that are not only technically interoperable but communicatively coherent across Europe.