Show more disputed lines for POV in low zooms

[nvkelso]

To solve "gaps" in the country boundary lines at low zooms sourced from Natural Earth, we need to be more liberal in NOT filtering by min_zoom all the time, just for that layer and features (country, disputed, region kinds in boundary layer).

Per nvkelso/natural-earth-vector#301 (comment):

Adjust min_zoom of disputed lines to be smaller when one or more of their claimants needs them earlier to complete their own country boundary line at lower zooms. See China along India, Pakistan, Bhutan salients.

The simplest thing to do is in QGIS (and for vector tiles) is to always include features from the scalerank theme (so remove the min_zoom filters) as for default the current min_zoom is ideal... but otherwise we'd need to include optional min_zoom_{pov} for all the POV and there are an insane number of columns as it is.

If we were to add various min_zoom_{pov} then downstream QGIS and vector tiles would need to take the minimum min_zoom_{pov}for inclusion at that zoom... but that's not something QGIS's basic layer filters are setup for, and the layer styling is already pretty complicated as it is.

[nvkelso]

Relevant code:

• min_zoom globals: https://github.com/tilezen/vector-datasource/blob/v1.8.0/yaml/boundaries.yaml#L6
• min_zoom remapping: https://github.com/tilezen/vector-datasource/blob/v1.8.0/yaml/boundaries.yaml#L9-L31
• kind remapping: https://github.com/tilezen/vector-datasource/blob/v1.8.0/yaml/boundaries.yaml#L33-L52
• NE config: https://github.com/tilezen/vector-datasource/blob/v1.8.0/yaml/boundaries.yaml#L225-L247

One way to do this is to split apart the disputed lines from the international boundary lines (this may need to be a little more sophisticated – for instance you could test if there is a fclass_xx that's not null):

  # ne
  - filter:
      featurecla:
        - 'International boundary (verify)'
        - 'Disputed (please verify)'
        - 'Indefinite (please verify)'
        - 'Indeterminant frontier'
        - 'Lease limit'
        - 'Line of control (please verify)'
        - 'Overlay limit'
        - 'Unrecognized'
        - 'Map unit boundary'
    min_zoom: { col: min_zoom }
    output:
      <<: *output_properties
      <<: *ne_localized_kind_properties
      kind: *ne_country_boundaries_kind
      kind_detail: '2'
    table: ne

# ne for disputed kind:xx POV we want to always include
# the disputed lines early so when that POV enables them
# the data is available in tiles
  - filter:
      featurecla:
        - 'Breakaway'
        - 'Claim boundary'
        - 'Elusive frontier'
        - 'Reference line'
    min_zoom: 1
    output:
      <<: *output_properties
      <<: *ne_localized_kind_properties
      kind: *ne_country_boundaries_kind
      kind_detail: '2'
    table: ne

[nvkelso]

This only should matter for the last 4 here:

        - [ 'disputed_breakaway', 'Breakaway' ]
        - [ 'disputed_claim', 'Claim boundary' ]
        - [ 'disputed_elusive', 'Elusive frontier' ]
        - [ 'disputed_reference_line', 'Reference line' ]

[nvkelso]

Test in this tile at zoom 4:

• 256 px sized zoom 4: https://tile.openstreetmap.org/4/11/6.png
• 512 px sized zoom 3: https://tile.openstreetmap.org/3/5/3.png

Right now there are no features with kind:cn = country and you want there to be some, and test the min_zoom being the new value of 1.

This zoom 5 feature, with these attributes (modulo min_zoom) should also be included at zoom 4:

Because Natural Earth 1:50m has this disputed boundaries in it and Tilezen uses from zoom 2, 3, 4 this will work.

The change would also set the min_zoom in the zoom 5 tiles from NE 1:10m to 1 as well, so you should also test that.

Because the NE 1:110m doesn't include disputed boundary lines at all in the upstream data, this is not testable at zoom 0 and 1. If we need to fix this at those zooms, we need an upstream NE data fix.

[peitili]

feature appears in newly build