Holding the line – non-locality in map rendering part 2

I had written about non-locality in tiled rule based map rendering in general some time ago and that post gathered quite a bit of interest – including renewed interest in OSM-Carto development for problems where non-locality is a long known issue. Here i want to continue more in depth on a specific aspect of this. The difficulty of aggregation The specific issue this post is about is the aggregation or merging of geometries in map rendering. As i mentioned in the previous post in the section on explicit non-localities in map design: Since geometries in OpenStreetMap are frequently split in a relatively fine grained fashion to differentiate attributes locally, it is often a problem to render the individual components separately, because it disrupts the rendering. For example, when a road is rendered based on relatively short segments in mapping, dashing patterns and labeling are going to be affected by this. So it might seem a good idea to simply merge all road elements within a tile…