[Talk-us] Heavily-wooded residential polygons

[stevea]

Fellow OSMer doug_sfba maps natural=wood edges around the southern and western areas of Silicon Valley (the South Bay Area in California), among other mapping and places.  I map similar things a bit further south, with initial emphasis on landuse, but as I sometimes combined natural tags in the same polygon, I now tend — as "more correct" — towards breaking these into two polygons, this is a fair bit of work.  Doug and I have collaborated a lot, and agree (among other things) that in OSM, there is a distinction between landUSE and landCOVER.  For example, "treed farmland" or "heavily wooded residential" prove slightly problematic to OSM tagging.  Due to complex tagging schemes on complex (multi)polygon construction (sometimes half-jokingly referred to as "higher math," though it is more like discrete math, topology and possibly its concept of "genus" or "holes in a complex surface") this can result in quite different results in the Carto renderer.

Recently, Doug and I discussed that Carto, areas of "heavily wooded residential" render with three possibilities, depending on some complex tagging strategies and the sizes of the underlying (multi)polygons:

• "fully gray," indicating pure residential, but leaving the human viewing Carto no indication the area is heavily wooded,
• "fully green-with-trees" (as natural=wood), which excludes the important aspect that while wooded, this is residential, or
• "gray with superimposed trees" (in both our opinions, a superior and pleasing method to display "heavily wooded residential").

For an example of the latter, see https://www.osm.org/query?lat=37.3769&lon=-122.2506#map=15/37.3873/-122.2526 and notice the residential areas surrounding Thornewood Open Space Preserve.

As I mentioned to Doug I exchanged a couple of emails with user:jeisenberg (a principal contributor to Carto) about what was going on with some examples of this, and Mr. Eisenberg explained to me (in short) that it is a complicated ordering (or re-ordering) of layers issue, both Doug and I continue to scratch our heads about what "best practice" might be here.  (For "heavily wooded residential" polygons, which are frequent in Northern California).  While Doug and I both tend towards the preference of the "superimposed look," it is not always simple to achieve, due to complexities in the renderer and data/tagging dependencies.  And, Doug and I are certainly aware of "don't code for the renderer."  However, given that Doug and I are fairly certain that others have noticed this, but aren't certain that others know what best to do (we don't, either), we ask the wider community "what do you think?" and "What are best practices here?"

Yes, the questions are a bit fuzzy and it is difficult to describe what is going on in the renderer (ordering or re-ordering of layers depending on size, I believe), but it does seem like we might be able to agree upon a best practice of "what to do."  In short, Doug and I both strive to "tag accurately," but just as "9" can be 5+4 or 6+3, there are many methods to combine and build polygons to describe an area and tag them accurately, though many combinations render differently.

This is being sent to both talk-us and the tagging list, where I think the latter may be a better place, but this was noticed by a couple of California mappers (for some time), so including talk-us might help widen the audience to include others who have noticed these anomalies.  Thank you in advance for good discussion.

SteveA
California