Basic simplestyle implementation

.gitignore

@@ -11,4 +11,7 @@ build/
 dist/
 .DS_Store
 .vscode
-*.db
+Pipfile
+!demo/Pipfile
+*.db
+node_modules

README.md

@@ -68,6 +68,34 @@ Options:
 - `tile_layer`: Use a URL template that can be passed to a [Leaflet Tilelayer](https://leafletjs.com/reference-1.7.1.html#tilelayer)
 - `tile_layer_options`: All options will be passed to the tile layer. See [Leaflet documentation](https://leafletjs.com/reference-1.7.1.html#tilelayer) for more on possible values here.
 
+## Styling map features
+
+Map features can be styled using the [simplestyle-spec](https://github.com/mapbox/simplestyle-spec). This requires setting specific fields on returned rows. Here's an example:
+
+```sql
+SELECT Name, geometry, "#ff0000" as fill, "#0000ff" as stroke, 0.2 as stroke-width,  from neighborhoods
+```
+
+That will render a neighborhood map where each polygon is filled in red, outlined in blue and lines are 0.2 pixels wide.
+
+A more useful approach would use the `CASE` statement to color features based on data:
+
+```sql
+SELECT
+  Name,
+  geometry,
+  CASE
+    Name
+    WHEN "Roslindale" THEN "#ff0000"
+    WHEN "Dorchester" THEN "#0000ff"
+    ELSE "#dddddd"
+  END fill
+FROM
+  neighborhoods
+```
+
+This will fill Roslindale in red, Dorchester in blue and all other neighborhoods in gray.
+
 ## Development
 
 To set up this plugin locally, first checkout the code. Then create a new virtual environment:

demo/Makefile

@@ -5,8 +5,15 @@ install:
 neighborhoods.geojson:
 	wget -O $@ https://opendata.arcgis.com/datasets/3525b0ee6e6b427f9aab5d0a1d0a1a28_0.geojson
 
-boston.db: neighborhoods.geojson
-	pipenv run geojson-to-sqlite $@ neighborhoods $^
+schools.geojson:
+	wget -O $@ https://bostonopendata-boston.opendata.arcgis.com/datasets/boston::public-schools.geojson
+
+boston.db: neighborhoods.geojson schools.geojson
+	pipenv run geojson-to-sqlite $@ neighborhoods neighborhoods.geojson
+	pipenv run geojson-to-sqlite $@ schools schools.geojson
 
 run: boston.db
 	pipenv run datasette $^ -m metadata.yml
+
+clean:
+	rm -f boston.db neighborhoods.geojson schools.geojson

demo/Pipfile

@@ -10,4 +10,4 @@ geojson-to-sqlite = "*"
 [dev-packages]
 
 [requires]
-python_version = "3.9"
+python_version = "3.10"

demo/metadata.yml

@@ -11,3 +11,21 @@ plugins:
       minZoom: 1
       maxZoom: 16
       ext: jpg
+
+databases:
+  boston:
+    queries:
+      color_by_name:
+        title: Color by name
+        sql: |
+          SELECT
+            Name,
+            geometry,
+            CASE
+              Name
+              WHEN "Roslindale" THEN "#ff0000"
+              WHEN "Dorchester" THEN "#0000ff"
+              ELSE "#dddddd"
+            END fill
+          FROM
+            neighborhoods