This article was originally written in French here. This English version was partly translated with DeepL.com.

OpenArdenneMap is an open-source map style designed for the production of topographic maps for printing. Based on OpenStreetMap data, it is available for use with QGIS and the Mapnik/cartoCSS libraries. Here is the winter 2025–26 release.

I started working on OpenArdenneMap about nine years ago. My aim was to create a map style for producing high-quality topographic maps intended for printing, using mainly OpenStreetMap data. The main challenge is to automate map production, to limit ‘manual’ corrections as much as possible (without eliminating them entirely). Since then, the style has been used in several mapping projects: together with colleagues, I have set up a website for downloading hiking maps (hiking.osm.be) and have been able to test the deployment of a tile server on https://www.nobohan.be/webmaps/oam-tile/.

One might think that, since it allows for the production of complete topographic maps, the development of a cartographic style in itself has reached its conclusion. This is not the case. I believe that the techniques and practices involved in developing topographic styles from OpenStreetMap data, in all their diversity and complexity, are still in their infancy. Recent years have seen the advent of numerous cartographic styles for on-screen maps, as well as the emergence of virtual tiles and 3d rendering. However, simple cartographic generalisation techniques and basic principles of cartographic semantics are rarely utilised in these new map styles.

This winter, I was able to draw on the work of a master’s student in geography, Noé Monjoie, to investigate these cartographic generalisation techniques in particular using OpenStreetMap data. The aim was to test algorithms for transforming geographical data to address certain representation issues in OpenArdenneMap (and in other digital cartographic styles). Only a very small part of his work has been incorporated into this new release. I hope the rest will follow in future updates. In the meantime, here are the new features of the “Winter 2025–26” version:

Avoiding label overlap between layers

Using the QGIS overlay_intersects() function, you can prevent labels from one layer from appearing on top of another. In this case, the aim is to prevent waterway labels from appearing within bodies of water. For reasons of hydrological continuity, OpenStreetMap contributors are encouraged to ensure that waterways feeding into bodies of water cross them from both sides. As the waterway segment is often interrupted at the boundary of the body of water, this causes a conflict between the labels of the water area and the waterway. A conflict that previously often resulted in the absence of labels for the water area.

Rendering of a culvert symbol

When a stream or drain passes under a road or path, this is a culvert, which differs from a bridge that provides a wider passage for the stream. This difference between a bridge and a culvert exists in OpenStreetMap data (tags bridge=yes vs tunnel=culvert). By using the orientation of the waterway segment passing through this culvert, as well as the entry and exit points of this passage, we arrive at this rendering indicating the culverts, a rendering directly inspired by Belgian IGN maps from the 1960s to the 1980s.

Bridge symbol rendering

Using the same principle, here is a rendering of small bridges (on paths) and boardwalks (differentiated by length) that takes into account the length of the bridge.

Grouping elements with QGIS clustering

Finally, an improvement based on Noé’s work, involving the clustering of certain point symbols (in this case, a picnic table) in QGIS. This was already handled well in Mapnik, but I hadn’t yet figured out how to do it in QGIS (in reality, it’s simply a symbology option for points).

Looking ahead, as mentioned earlier, Noé’s work has opened up several possibilities for data generalisation that I hope to be able to implement. Finally, QGIS 4 is due out this year, and so the new features brought by this major new version of QGIS will inevitably help OpenArdenneMap to evolve.