I'm trying to build isochrones for some schools, to understand the accessibility. My mode of travelling is "walk" and I wanted to create a list of at least 2 travel times, 30 minutes and 1 hour.
Here below is my code:
# import required libraries
import pandas as pd
import geopandas as gpd
import matplotlib.pyplot as plt
import networkx as nx
import osmnx as ox
from descartes import PolygonPatch
from shapely.geometry import Point, LineString, Polygon
from IPython.display import IFrame
import folium
import itertools # will be used to perform feature joining
# %matplotlib inline
ox.__version__
# function to get isochrones
def get_isochrone(lon, lat, walk_time=[30,60], speed=4.5):
loc = (lat, lon)
G = ox.graph_from_point(loc, simplify=True, network_type='walk')
# Create nodes geodataframe from Graph network (G)
gdf_nodes = ox.graph_to_gdfs(G, edges=False)
x, y = gdf_nodes['geometry'].unary_union.centroid.xy
center_node = ox.get_nearest_node(G, (y[0], x[0]))
meters_per_minute = speed * 1000 / 60 #km per hour to m per minute
for u, v, k, data in G.edges(data=True, keys=True):
data['time'] = data['length'] / meters_per_minute
# get one color for each isochrone
iso_colors = ox.plot.get_colors(n=len(walk_time), cmap="plasma", start=0, return_hex=True)
# color the nodes according to isochrone then plot the street network
node_colors = {}
for walks_time, color in zip(sorted(walk_time, reverse=True), iso_colors):
subgraph = nx.ego_graph(G, center_node, radius=walks_time, distance="time")
for node in subgraph.nodes():
node_colors[node] = color
nc = [node_colors[node] if node in node_colors else "none" for node in G.nodes()]
ns = [15 if node in node_colors else 0 for node in G.nodes()]
# make isochrone polygons
isochrone_polys = []
for trip_times in sorted(walk_time, reverse=True):
subgraph = nx.ego_graph(G, center_node, radius=trip_times, distance="time")
node_points = [Point(data['x'], data['y']) for node, data in subgraph.nodes(data=True)]
polys = gpd.GeoSeries(node_points).unary_union.convex_hull
isochrone_polys.append(polys)
# adding color
for polygon, fc in zip(isochrone_polys, iso_colors):
patch = PolygonPatch(polygon, fc=fc, ec="none", alpha=0.6, zorder=-1)
# isochrone_polys.add_patch(patch)
return isochrone_polys
When I call the get_isochrone function:
# calling the function with the coordinates
map = coordinates.apply(lambda x: get_isochrone(x.longitude, x.latitude), axis=1)
What is returned is a list of polygons with each school point having polygons equal to the number of items in the travel times list. I however noticed that the polygons returned for each point are exactly the same.
Just to verify: This script shows that they are the same:
for i in map:
print(i[0])
print(i[1])
print('\n')
Here are the results:
As you can see, each school point returns two polygons with exactly the same coordinates, for different travel times. I have reviewed the python function several times, even changed the travel time to one item in the travel time list like 100, and I still get exactly the same coordinates. I may have missed something and I'll appreciate any help. Thanks!
In addition, I also realized that the add_patch() method in the function adds color to the plot_graph() only. How can I add the colors to the polygons in the Folium map?
