Currently, river areas (`natural=water` + `water=river`) are rendered in the tiles as `class=river`. However, canal, stream, ditch, and drain water areas are rendered as `class=lake`. Since these types of objects are all flowing water, they should be grouped together into `class=river`, which allows for styles that render flowing water differently to do so on a consistent basis.
This PR proposes to add a new class, "pond" to the water layer, which allows for a style to de-emphasize minor bodies of water (tagged `water=pond,basin,wastewater`) when compared to more significant objects tagged reservoir/lake. This PR retains the default behavior of classifying a water body as a "lake" if more specific tagging is not added.
This PR adding OSM ID to the lakes
OSM lakes are used from zoom 6
From zoom 0 to zoom 5 are used Natural Earth lakes.
- There is a new joining mat. view (`match_osm_ne_id`) contains which Natural Earth ID should convert to OSM ID. This logic is used to keep a consistent ID between switching between NE (zooms 0 - 5) and OSM (zooms 6 - 12). For smaller areas (not the whole planet), where are not available OSM lakes, the NE lakes keep their NE ID.
- There are also switch the final views to the mat. views - this should slightly increase performance (get rid of multipolygons).
- FIX typo for zooms 0 - 3 (`lakes` instead of `lake`).
This PR removes an unnecessary check in water.yml.
generated SQL before:
```
SELECT CASE
WHEN waterway='riverbank' THEN 'river'
WHEN "waterway" = 'dock' THEN 'dock'
WHEN "water" = 'river'
OR "waterway" = 'riverbank'
THEN 'river'
WHEN "waterway" = '' THEN 'lake'
ELSE 'lake'
END;
```
generated SQL after:
```
SELECT CASE
WHEN waterway='riverbank' THEN 'river'
WHEN "waterway" = 'dock' THEN 'dock'
WHEN "water" = 'river'
OR "waterway" = 'riverbank'
THEN 'river'
ELSE 'lake'
END;
```
The `waterway=''` test is purely redundant because it returns the same value as the fall-through ELSE case: `lake`.
Simplify some of the OSM->OMT field value mappings using declarative syntax.
This approach is not for all cases, but in many it removes
the need of storing the same field in both the .yaml and .sql files.
TODO: support more complex AND/OR cases
