Zoom in - zoom out challenge: Semantically and visually coherent overview geological maps of Poland

Standardisation of geological maps visualisation is crucial for improving data legibility and comparison across different scales and regions. In Poland, overview geological maps ranging from scales of 1:2,500,000 to 1:500,000 have been traditionally prepared using distinct graphical styles, each tailored to the particular characteristics of the mapped geological units. These maps used to employ individual patterns and colour palettes to enhance the visibility and readability of geological features, prioritising the requirements of printed editions. However, differences in the number and types of geological units across various maps led to inconsistent visual representations, limiting the ease of comparison between them.

To address the above, the Polish Geological Institute’s team embraced the idea of creating a unified, semantically harmonised graphical style for overview geological maps. The main objective was to develop a common style for all stratigraphic units, which could be applied across various maps of Poland, particularly those prepared for online publication in the frame of the Polish Geological Cartograhy Platform. This experiment aimed to standardise the colour and pattern schemes, building upon the stratigraphic classification system provided by the International Commission on Stratigraphy (ICS), but with necessary extensions to accommodate mixed stratigraphy.

While this approach slightly reduced the visibility of details in certain areas, it significantly enhanced the comparability of geological data across maps. By adopting a consistent visual language, the maps delivered a clearer cartographic message, particularly when zooming in and out in map viewers. The harmonisation of the graphical style also enhanced data visualisation across various scales, making it easier for geologists to interpret and compare geological units.

This initiative was inspired by earlier efforts, such as the OneGeology initiative and the INSPIRE Directive, both of which sought to standardise the visualisation of lithological and stratigraphic data. However, these frameworks primarily focused on older geological units and their principal lithologies, which could lead to potential misinterpretations of the data. For example, geological units spanning from the Cambrian to the Devonian period were often represented using a single colour, which could obscure their true geological diversity. To address this, PGI team proposed the use of distinct colours for each geological period, drawing inspiration from the Commission for the Geological Map of the World (CGMW) colour codes.

The results of this experiment demonstrate that a semantically harmonised approach to geological map visualisation not only enhances the clarity of individual maps but also makes data more comparable across different scales and regions. By providing a consistent and intuitive visual representation of geological units, this method helps to improve the overall understanding of geological data and facilitates its use in various scientific, educational, and practical contexts.