updates docs and create test for canal change (#2100)

* update docs and create test for canal change
* Fixed test

Author: jeffdefacto

docs/layers.md

@@ -2468,7 +2468,7 @@ However, if the roads layer does not include `linear_ref_id`, then it should be
 
 Water `polygons` representing oceans, riverbanks and lakes. Derived from a combination of the `waterway`, `natural`, and `landuse` OpenStreetMap tags. Includes coastline-derived water polygons from [osmdata.openstreetmap.de](https://osmdata.openstreetmap.de) and inland water directly from OpenStreetMap at higher zoom levels 8+, and [Natural Earth](http://naturalearthdata.com) polygons at lower zoom levels (0-7). Water polygons are progressively added based on an area filter until all water is shown at zoom 16+. Covered water is not included.
 
-Also includes water `line` geometries for river and stream centerlines and "label_position" `points` for labeling polygons de-duplicated across tile boundaries. OpenStreetMap sourced waterway lines kinds of `river`, `canal`, and `stream` are included starting at zoom 11 and `ditch`, `drain` (zoom 16+).
+Also includes water `line` geometries for river and stream centerlines and "label_position" `points` for labeling polygons de-duplicated across tile boundaries. OpenStreetMap sourced waterway lines with kinds of `river`, and `canal` with the tag `boat` = `yes` (aka navigable canals) are included starting at zoom 9, `stream` and other `canal` features are included starting at zoom 11, and `ditch`, `drain` (zoom 16+).
 
 Tilezen calculates the composite exterior edge for overlapping water polygons and marks the resulting line `boundary=true`. Set to `true` when present on `line` geometry, or from Natural Earth line source.
 

integration-test/2098-canal-min-zoom.py

@@ -0,0 +1,46 @@
+import dsl
+
+from . import FixtureTest
+
+
+class TestCanalMinZoom(FixtureTest):
+    def test_canal(self):
+        z, x, y = (16, 10483, 25332)
+        self.generate_fixtures(
+            dsl.way(76287073, dsl.tile_box(z, x, y), {
+                'name': 'Ridenbaugh High Line Canal',
+                'boat': 'no',
+                'waterway': 'canal',
+                'source': 'openstreetmap.org'
+            })
+        )
+
+        self.assert_has_feature(
+            z, x, y, 'water',
+            {'id': 76287073,
+             'name': 'Ridenbaugh High Line Canal',
+             'kind': 'canal',
+             'min_zoom': 11,
+             'source': 'openstreetmap.org'})
+
+    def test_boat_canal(self):
+        z, x, y = (16, 10483, 25332)
+        self.generate_fixtures(
+            dsl.way(85123623, dsl.tile_box(z, x, y), {
+                'name': 'Canal de Bourgogne',
+                'access': 'boat',
+                'boat': 'yes',
+                'fishing': 'yes',
+                'waterway': 'canal',
+                'source': 'openstreetmap.org'
+            })
+        )
+
+        self.assert_has_feature(
+            z, x, y, 'water',
+            {'id': 85123623,
+             'name': 'Canal de Bourgogne',
+             'kind': 'canal',
+             'boat': 'yes',
+             'min_zoom': 9,
+             'source': 'openstreetmap.org'})