Enabling loading from TransportationNetworks

[RicoFio]

Description

This PR implements the feature enhancement suggested in #47. It enables City2Graph to download data from the TransportationNetworks repository and convert it into a networkX graph. I haven't added it yet to the documentation since I first wanted to check whether this should go into a separate file.

Usage

from city2graph.data import load_transportation_networks_data
from city2graph import gdf_to_nx
import geopandas as gpd
import networkx as nx
from shapely.geometry import LineString
import pandas as pd
from matplotlib import pyplot as plt

data = load_transportation_networks_data('SiouxFalls')

nodes = gpd.GeoDataFrame(data['nodes'], geometry=gpd.points_from_xy(data['nodes']['x'], data['nodes']['y']), crs="EPSG:4326")
edges = gpd.GeoDataFrame(data['network'], geometry=None)
# Create geometry for edges using from_node and to_node coordinates
edge_geometries = []
edge_indices = []

for _, edge in edges.iterrows():
    from_node = nodes[nodes['node'] == edge['init_node']].iloc[0]
    to_node = nodes[nodes['node'] == edge['term_node']].iloc[0]

    line = LineString([from_node.geometry.coords[0], to_node.geometry.coords[0]])
    edge_geometries.append(line)
    edge_indices.append((edge['init_node'], edge['term_node']))

edges = gpd.GeoDataFrame(
    edges,
    geometry=edge_geometries,
    index=pd.MultiIndex.from_tuples(edge_indices, names=['u', 'v']),
    crs="EPSG:4326"
)
graph: nx.DiGraph = gdf_to_nx(nodes, edges, directed=True)
pos = {row['node']-1: (row['x'], row['y']) for _, row in nodes.iterrows()}
nx.draw(graph, pos, with_labels=True, node_size=80, font_size=8, arrows=True)
plt.show()

Checklist

• I have read the Contributing Guide.
• I have updated the documentation, if necessary.
• I have added tests to cover my changes.
• All new and existing tests passed.
• Pre-commit checks passed locally.