[MichaelKreil]

As discussed in #184, this should be included in version 1.2.

Problem:

Some features in the streets layer can only be distinguished by an attribute, but the schema lists that attribute for a higher zoom level than the feature itself. Between these two zoom levels, features end up in tiles with the wrong attribute because it is missing.

Link roads (kind=motorway/trunk/primary/secondary/tertiary):

• in layer from zoom level 5+/6+/8+/9+/10+
• links are identified by attribute link
• but the attribute was available from: 11+ (shortbread 1.0, 1.1)
• now the attribute is available from: 5+ (shortbread 1.2)

Railways with service=* (kind=rail/narrow_gauge):

• in layer from zoom level 10+
• identified by attribute service
• but the attribute was available from: 11+ (shortbread 1.0, 1.1)
• now the attribute is available from: 10+ (shortbread 1.2)

As a result, motorway links are drawn as stumps of main roads below z11. At z10, railway yards, sidings, and spurs are drawn at main-line weight, and then switch to service styling at z11.

Change

In schema/1.2.md, layer streets:

• link: zoom 11+ -> 5+, the lowest zoom where any link road appears
• service: zoom 11+ -> 10+, the lowest zoom level at which railways with service=* appear

Impact on implementations

These changes affect the data, not just the documentation. TileMaker and the OSM2PGSQL Themepark shortbread_v1 theme split the layer into streets_low (z5–10, only kind and rail), streets_med and streets. They need to add link and service to the streets_low writes. In TileMaker, this involves a two-line change. The Planetiler custommap sample requires a matching zoom change.

What this does not fix

This PR is not a "hot fix" for the 1.0 and 1.1 specifications. Tiles built against these specifications will still contain incorrect data with erroneous attributes at certain zoom levels.