I recently worked on a number of map design matters in my OSM-Carto derivative, which i have not discussed here on the blog yet. Much of this is related to point symbols, with – so far – a thematic focus on human physical constructions of various kinds.

In OSM-Carto point symbol rendering got kind of stuck several years ago because we could not reach a consensus strategy on how to deal with a number of fundamental challenges we were faced with – both technically and design wise. I have shown here new methods to overcome these challenges. And i have demonstrated how these methods can be used to expand the differentiation of point features displayed while remaining intuitively understandable. In this post i want to further build on that.

The class of features i am going to look at is point barriers. I have worked on line barriers before – with more differentiated display and ground unit rendering and i have also shown visualization one specific point barrier feature (barrier=entrance) by modifying the display of line barriers and cutting out the entrance from those – showing the point feature purely through the modification of its context. In a similar fashion i have shown contextualized rendering of fords and mountain passes through local modification of the line signature of the road they are located on. And i have shown, among other things, use of symbol variations and context based adjustments for entrance nodes of buildings.

Point barrier rendering through pictorial symbols has been a feature of OSM-Carto since the beginning. The original implementation featured distinct symbols for barrier=gate and barrier=lift_gate:

These symbols have – with slight modifications – remained trademark features of OSM-Carto. And they have, over the years, been extended with additional symbols, mostly ad hoc and non-systematically, for other point barriers. This created several problems:

• symbols are very inconsistent in size, sometimes in a counter-intuitive way so that larger symbols are used to depict physically smaller features than those represented by smaller symbols.
• some symbols have an integrated white halo while others are plain color – leading to very different appearances on backgrounds of different color.
• some symbols are hard to recognize in situations where it is not clear from context what they mean. This in particular applies to the cycle barrier symbol.

The lack in stylistic consistency is the main thing i intended to address. Beyond that i added more differentiation in terms of different barrier variants. I also introduced differentiation between restricted access barriers and those that everyone can cross freely for some barrier types.

I maintain the duality in symbol styles with some symbols depicting the barrier in question from top while others showing a profile view. This is hard to avoid since some types of barrier do not have a discernible visual footprint from top while others are most unique in appearance from top (like turnstile, kissing_gate). For the symbols showing the barrier from top i show the symbol rotated by 90 degrees depending on the context of line barriers and roads/paths at the barrier node. For small, pixel aligned symbols like these a free rotation is not possible without largely sacrificing readability. But a 90 degree rotation makes it often much easier to intuitively understand the symbol.

Here is the full set of new point barrier depictions at the different zoom levels.

The second symbol shown is either the variant for restricted access barriers (top part of the table) or the 90 degree rotated variant.

Many of the symbols have a slightly smaller variant used for the lower zoom levels and a slightly larger version shown on the higher levels

All symbols except those for bollards are consistently shown with a thin white halo that is dynamically generated during rendering.

Three real world examples for the new rendering:

Conclusions

I showed here how a consistent design paradigm (which builds on the original design concepts of early barrier rendering in OSM-Carto from more than 10 years ago) allows rendering a large variety of different point features with differentiated symbols while remaining largely intuitively readable. I demonstrated 20 different base classes of point barriers with 4 access restricted variants and 7 context dependent 90 degree rotated variants. Nearly all of these symbols, in addition, have a simplified lower zoom level design, in some cases aggregating several similar barrier types into one design.

Technically, this relies on the symbol and label rendering framework i had introduced in the AC-Style previously and that scales much better with a larger number of design variants than hand writing lengthy MSS as it is used in OSM-Carto so far.