Simplify routes prior to sending to Django template (#124)

* Add layer toggle to map

Following official Leaflet tutorial closely:
https://leafletjs.com/examples/layers-control/

Separate out commands to instantiate map layers from commands
to add them to map.

Create a "control" object whose "overlayMaps" parameter
determines which features can be toggled on or off.

For now, set all "stations" as one toggle-able feature, and
all "routes" as another.

TODO: separate out different station/route layers based on
mode of transit and/or line of interest. This would likely
involve initializing distinct layers (e.g. busStations,
railStations, busRoutes...) and then using conditional logic
(perhaps relying on passing in the `route_type` GTFS number)
to determine what goes where

* Respond to black failure notification by running black on two files

Weirdly these weren't files I edited in any way prior to previous
commit

* Get simplified routes working

---------

Co-authored-by: Matthew Jackson <mbjackson@Matthews-MacBook-Air.local>

app/route_rangers_api/views.py

@@ -8,6 +8,7 @@
 from django.utils import timezone
 from django.core.serializers import serialize
 from django.templatetags.static import static
+from django.contrib.gis.geos import GEOSGeometry, MultiLineString, LineString
 
 
 from app.route_rangers_api.utils.city_mapping import CITY_CONTEXT
@@ -35,12 +36,18 @@ def dashboard(request, city: str):
     # get commute
 
     # get paths
-    routes = TransitRoute.objects.filter(city=CITY_CONTEXT[city]["DB_Name"])  # .values(
-    # MultiLineString needs to be serialized into a GeoJson object for Leaflet to
-    # work with it.
-    # to serialize into GeoJson, need to get out entire Django model object, not just
-    # the .values("geo_representation", "route_name", "color")
-    # with .values() you get "AttributeError: 'dict' has no component 'meta'"
+    routes = TransitRoute.objects.filter(city=CITY_CONTEXT[city]["DB_Name"])
+    # reduce load time and data transfer size by overwriting model attribute
+    TOLERANCE = 0.00005
+    for route in routes:
+        simple_geo_representation = route.geo_representation.simplify(
+            tolerance=TOLERANCE, preserve_topology=True
+        )
+        # simplify() might alter the GEOS type; can't allow that
+        if isinstance(simple_geo_representation, LineString):
+            simple_geo_representation = MultiLineString(simple_geo_representation)
+        route.geo_representation = simple_geo_representation
+
     routes_json = serialize(
         "geojson",
         routes,
@@ -49,6 +56,8 @@ def dashboard(request, city: str):
     )
 
     # stations
+    # TODO: consider passing these in with serialized geoJSON instead of
+    # creating lst_coords separately
     stations = TransitStation.objects.values().filter(
         city=CITY_CONTEXT[city]["DB_Name"]
     )