The tag `landuse=park` is a rare tagging mistake of `leisure=park`. The OSM wiki [lists this tag as a mistake](https://wiki.openstreetmap.org/wiki/Tag:leisure%3Dpark). It is included in the landcover layer with a note that there were (at the time) 600 parks tagged in this way. There are currently a bit over 100 objects tagged with this mistake. Based on the wiki documentation and obvious decline of this tag, we should remove it so that we're not introducing mapping mistakes into the database and not inadvertently providing mapper feedback that encourages the use of mistake tagging.
Instead of using [Douglas-Peucker algorithm](https://postgis.net/docs/ST_SimplifyPreserveTopology.html) which is using for generalized tables [imposm](https://imposm.org/docs/imposm3/latest/mapping.html#generalized-tables) it is used [Visvalingam-Whyatt algorithm](https://postgis.net/docs/ST_SimplifyVW.html).
Solution:
remove imposm generalized tables (during `import-osm`) and create generalization in `import-sql` step for zooms 7-14. Zooms 0-6 are from Natural Earth data.
Upper zoom levels (7 and 8) are ok to merge with no big impact on creation speed. In Canada from z9 it took too long. Between zoom levels 10 - 13 there can be union polygons with less than 300 edge points (empirical number based on a test on Canada forest, can be discussed). Polygons with more than 300 edge points are just simplified. Zoom 14 is from the original dataset `osm_landcover_polygon`.
There is also removed `osm_id` which is never used and not passed into vector tiles.
quicker and cleaner diagram image generation.
Remove etl-graph and mapping-graph targets - redundant
Also, the obsolete "fields" is still in Imposm's code and both names are accepted,
but "fields" is not documented anywhere (PR submitted), and could be removed at any moment.
Our docs were not supporting it until this PR, so renaming it at the same time.
Several images have been updated due to a more inclusive mapping scan
Requires https://github.com/openmaptiles/openmaptiles-tools/pull/147 (merged)
Jeroen Hoek