Reduce size of roads layer at zooms 10 and 11

[nvkelso]

There are a lot of random (orphaned) unclassified and residential road segments included at zooms 10 and 11 in dense cities. These seem to be "bike" related.

Fix in in 5 parts.

Zoom 10 in London (256px tile size or 512px at 10/511/340 for research):

Zoom 11 in London

Zoom 12 in London

Zoom 10 in Paris: (256px tile size):

Zoom 11 in Paris

Zoom 12 in Paris

Part of this stems from #1250 and #1462, which solved for the rural unclassified case where those are actually regional connectors. But in the process too many random tiny urban roads (especially in Europe see London and Paris) were added. That min_zoom of 11 should be reverted to 12, those tests updated, and documentation changed.

Specifically:

• vector-datasource/yaml/roads.yaml

  Line 397 in 024909e

  min_zoom: { clamp: { min: 0, max: 11, value: { call: { func: mz_calculate_path_major_route, args: [ { col: fid }, { col: meta.relations } ] } } } }

    min_zoom: { clamp: { min: 0, max: 12, value: { call: { func: mz_calculate_path_major_route, args: [ { col: fid }, { col: meta.relations } ] } } } }

Some of the other roads are bike or walking related, where they get promoted up a zoom or two depending on what type or bicycle or walking relation (international, national, regional, and local) it's a member of, via #1172 and #1198.

This was done for Walkabout map style at Mapzen, but introduces extra features for a general purpose map. Let's relax those a single zoom, per https://github.com/tilezen/vector-datasource/blob/master/docs/SEMANTIC-VERSIONING.md#minor-version-increments to keep with MINOR version change.

The code to change is:

• vector-datasource/data/functions.sql

  Lines 678 to 701 in 15a8fb3

  	CREATE OR REPLACE FUNCTION mz_calculate_path_major_route(osm_id BIGINT, dummy INTEGER)
  	RETURNS SMALLINT AS $$
  	BEGIN
  	RETURN (
  	SELECT
  	MIN(
  	CASE WHEN hstore(tags)->'network' IN ('icn', 'ncn') THEN 8
  	WHEN hstore(tags)->'network' IN ('iwn', 'nwn') THEN 9
  	WHEN hstore(tags)->'network' IN ('rcn') THEN 10
  	WHEN hstore(tags)->'network' IN ('rwn') THEN 11
  	WHEN hstore(tags)->'network' IN ('lcn') THEN 11
  	WHEN hstore(tags)->'network' IN ('lwn') THEN 12
  	ELSE NULL
  	END
  	)
  	AS p
  	FROM planet_osm_rels
  	WHERE
  	parts && ARRAY[osm_id] AND
  	parts[way_off+1:rel_off] && ARRAY[osm_id] AND
  	mz_is_path_major_route_relation(hstore(tags))
  	);
  	END;
  	$$ LANGUAGE plpgsql STABLE;

Specifically:

            CASE WHEN hstore(tags)->'network' IN ('icn', 'ncn') THEN 8
                 WHEN hstore(tags)->'network' IN ('iwn', 'nwn') THEN 9
                 WHEN hstore(tags)->'network' IN ('rcn') THEN 11
                 WHEN hstore(tags)->'network' IN ('rwn') THEN 11
                 WHEN hstore(tags)->'network' IN ('lcn') THEN 12
                 WHEN hstore(tags)->'network' IN ('lwn') THEN 12

Additionally we should drop more feature properties at zoom 12, too (changing 12 to 13), to allow more feature merging at zoom 11 and 12:

• drop name and networks to 12 not 11: https://github.com/tilezen/vector-datasource/blob/master/queries.yaml#L1237-L1241
• drop early highway names to 12 not 11: https://github.com/tilezen/vector-datasource/blob/master/queries.yaml#L1253-L1257
• drop bus networks info from 12 not 11: https://github.com/tilezen/vector-datasource/blob/master/queries.yaml#L1282-L1286
• many road properties to 13 not 12: https://github.com/tilezen/vector-datasource/blob/master/queries.yaml#L1012-L1017
• name and ref for paths to 13 not 12: https://github.com/tilezen/vector-datasource/blob/master/queries.yaml#L1079-L1083
• lists of networks to 13 not 12: https://github.com/tilezen/vector-datasource/blob/master/queries.yaml#L1308-L1312
• regional cycle networks to 12 not 11: https://github.com/tilezen/vector-datasource/blob/master/queries.yaml#L1345-L1349
• regional cycle networks to 13 not 12: https://github.com/tilezen/vector-datasource/blob/master/queries.yaml#L1355-L1359
• drop names on short boundaries to 12 not 11: https://github.com/tilezen/vector-datasource/blob/master/queries.yaml#L758-L762

Finally, we should drop surface tags from minor roads and paths at early zooms:

We do a transform here:

• https://github.com/tilezen/vector-datasource/blob/master/queries.yaml#L1136-L1146

Right after that we should dup the logic for

• https://github.com/tilezen/vector-datasource/blob/master/queries.yaml#L1116-L1130

And apply that to minor roads and paths until zoom 14.

 # drop these "detail" tags to get better merging at zoom < 14
  - fn: vectordatasource.transform.drop_properties
    params:
      source_layer: roads
      start_zoom: 0
      end_zoom: 14
      properties:
        - surface
      where: >-
        kind == 'minor_road' or 
        (kind == 'path' and zoom < 13)

We should drop more properties from all kinds of roads, too:

• https://github.com/tilezen/vector-datasource/blob/master/queries.yaml#L1094-L1114

Something more like:

 - fn: vectordatasource.transform.drop_properties
    params:
      source_layer: roads
      start_zoom: 0
      end_zoom: 15
      properties:
        - network
        - shield_text
        - bicycle_shield_text
        - bus_shield_text
        - walking_shield_text
        - hgv_restriction_shield_text
      where: >-
        (kind_detail == 'motorway' and zoom <  7) or
        (kind_detail == 'trunk' and zoom <  9) or
        (kind_detail == 'primary' and zoom <  11) or
        (kind_detail == 'secondary' and zoom <  12) or
        (kind_detail == 'tertiary' and zoom <  13) or
        (kind_detail == 'motorway_link' and zoom <  13) or
        (kind_detail == 'trunk_link' and zoom <  13) or
        (kind_detail == 'primary_link' and zoom <  14) or
        (kind_detail == 'secondary_link' and zoom <  14) or
        (kind_detail == 'tertiary_link' and zoom <  14) or
        (kind == 'minor_road' and zoom < 15) or
        (kind == 'path' and zoom < 14) or
        (kind == 'rail' and zoom < 15)

- fn: vectordatasource.transform.drop_properties
    params:
      source_layer: roads
      start_zoom: 0
      end_zoom: 15
      # short-hand for "name" property in the list below means all name-like
      # properties.
      all_name_variants: true
      properties:
        - name
        - ref
        - all_networks
        - all_shield_texts
        - service
        - access
        - osm_relation
      where: >-
        (kind == 'highway' and zoom <  11) or    
        (kind_detail == 'trunk' and zoom <  12) or
        (kind_detail == 'primary' and zoom <  13) or
        (kind_detail == 'secondary' and zoom <  14) or
        (kind_detail == 'tertiary' and zoom <  14) or
        (kind_detail == 'motorway_link' and zoom <  14) or
        (kind_detail == 'trunk_link' and zoom <  14) or
        (kind_detail == 'primary_link' and zoom <  15) or
        (kind_detail == 'secondary_link' and zoom <  15) or
        (kind_detail == 'tertiary_link' and zoom <  15) or
        (kind == 'minor_road' and zoom < 15) or
        (kind == 'path' and zoom < 14) or
        (kind == 'rail' and zoom < 15)

 - fn: vectordatasource.transform.drop_properties
    params:
      source_layer: roads
      start_zoom: 0
      end_zoom: 15
      properties:
        - service
        - surface
        - cycleway
        - cycleway_right
        - cycleway_left
        - walking_shield_text
        - hgv
        - operator
      where: >-
        (kind == 'highway' and zoom <  12) or
        (kind == 'major_road' and zoom <  13) or
        (kind == 'minor_road' and zoom < 15) or
        (kind == 'path' and zoom < 14) or
        (kind == 'rail' and zoom < 15)

[nvkelso]

This will require changes to the original Mapzen house styes, like tangrams/bubble-wrap#279.

[nvkelso]

Closed via #2008.