support `landuse=civic_admin` and related `landuse`

[alexlancaster]

This PR supports the landuse=civic_admin tag by rendering using a light blue background using the same styling as the Tracestack Topo layer

Fixes #2985

Changes proposed in this pull request:

• adds a light blue background with a thin border at higher zoom levels (z>17)
• supports the same colour for landuse= for civic_admin (an in-use tag) as well as institutional, government and governmental

Test rendering using local Kosmtik docker container:

• Boston Government Center: https://www.openstreetmap.org/#map=18/42.36249/-71.06250

  • Before (z18)

  

  • After (z18)

  

  • After (z16)

  

  • After (z19)

  

[imagico]

Thanks for the pull request.

This change suggests to render the following tags in a unified design with a semi-transparent blue-green fill and a matching thick outline, similar to the ones used for marinas/theme parks but rendered in the landcover layer:

• landuse=civic_admin
• landuse=institutional
• landuse=government
• landuse=governmental

I see a number of issues with that:

The tags suggested to be rendered are IMO not suitable to be rendered in this style at this time. Specifically:

• landuse=civic_admin has <900 uses, very sparse documentation
• landuse=institutional has 1667 uses, is clearly indicated to be a disputed tag and is based on the very vague English language term 'institution' without a clear language independent definition
• landuse=government has 516 uses and is undocumented
• landuse=governmental has 505 uses, only has a proposal page on the wiki and is almost exclusively used in China

All four tags massively overlap in their meaning and we have the general principle not to introduce new rendering of synonyms in this style. As the documentation of landuse=commercial correctly states, mappers widely use this tag also for government/administrative areas. There is no consensus that using any of the above tags instead is a more desirable way of tagging.

In terms of rendering it is also significant to note that office=government (263k uses) - with a further differentiation tag government=* (115k uses) - is the more widespread (and more broadly accepted) way to map specifics about administrative infrastructure. Rendering such in a differentiated form would be more significant for us. Also keep in mind that much administrative infrastructure is building-only with no area outside the building being part of a specific land use. Such cases would not show up with landuse rendering and such rendering could incentivize mappers to draw arbitrary wrapper polygons for the visual effect.

Regarding the design proposed - independent of the tagging this has the following issues:

• we don't want to use transparency in polygon fill colors because it leads to arbitrary and confusing color mixing with other colors.
• use of blue-green fill colors for something not vegetation or water related is problematic in terms of color systematics. All our generic urban landuse colors are in the range of weak red-purple-violet tones and were carefully designed in perceptual color space to form a harmonic set (see #599). Adding to that with an unrelated color is very confusing for the map user.
• heavy outline rendering in a semi-transparent blue is problematic because
  • depending on the background it can be confused with various other line signature, in case of blue color in particular with waterways.
  • it indicates a meaningful boundary where practically there is often none.
  • it hides actual mapping of physical boundaries (wall, fence etc.)
  • it looks weird in cases when urban landuse is split in mapping (which is widely considered a perfectly correct form of mapping for urban landuse)
  • rendering it in the landcover layer leads to it being covered by almost everything else - including other landuse fills, which leads to confusingly interrrupted line signatures.
  • overall this is a very heavy way of rendering polygons, which is not very suitable for a feature-rich style like ours.
• our systen of generic urban landuse rendering is already at the edge of being too complex to be intuitively understandable. Hence if we'd introduce rendering of additional tags we would need to aggregate them further (like combining them with existing landuse=commercial). This is of course only feasible if they have a well defined meaning and are well delineated from other tags in the first place.

Bottom line: I don't think any of the suggested tags currently qualifies for being rendered here and especially not all of them together as synonyms. And if, at one point in the future, this changes we would need to choose a design that harmonically integrates with our existing urban landuse rendering.

Side note: The rendering sample does not seem to match the current mapping - the polygon with the landuse tagging is this: https://www.openstreetmap.org/way/814380638 and i don't see the origin of the inner yard outlining shown.