mapping_utils.py

def load_map(place: str, graph_only: bool = False) -> (nx.MultiDiGraph, dict):
    """
    Load OSM trail data for a given region. Initially check if the graph has already been cached on disk, otherwise it will be downloaded.
    Args:
        place: The geocode of the region of interest, e.g. 'Shenandoah National Park, Virginia, USA'
        graph_only: If true, return only the NetworkX graph, not the geojson.

    Returns: The dataset as a NetworkX MultiGraph, the nodes geojson, the edges geojson

    """
    filename = p.sub("", place).lower().replace(" ", "_")
    graph_fp = f"static/graphs/{filename}.graphml"
    edges_fp = f"static/edges/{filename}.geojson"
    nodes_fp = f"static/nodes/{filename}.geojson"
    try:
        G = ox.load_graphml(graph_fp)
        print("Graph loaded from disk")
    except FileNotFoundError:
        print("Downloading and caching graph from OSM")
        # custom filter to only include walkable segments - see: https://support.alltrails.com/hc/en-us/articles/360019246411-OSM-Derivative-Database-Derivation-Methodology
        cf = '["highway"~"path|track|footway|steps|bridleway|cycleway"]'
        G = ox.graph_from_place(place, custom_filter=cf)
        ox.save_graphml(G, graph_fp)
    if graph_only:
        return G
    if os.path.isfile(edges_fp) is False or os.path.isfile(nodes_fp) is False:
        # convert Graph to GeoDataFrames and save as GeoJSON
        nodes, edges = ox.graph_to_gdfs(G)
        edges = edges[["name", "geometry", "length"]]
        edges["name"] = edges["name"].apply(lambda x: x[0] if type(x) is list else x)
        edges.to_file(edges_fp)
        nodes.to_file(nodes_fp)
    with open(nodes_fp, "r") as f:
        nodes = json.load(f)
    with open(edges_fp, "r") as f:
        edges = json.load(f)
    for feat in edges["features"]:
        # add custom tooltip property for Leaflet visualization
        tooltip = f"{feat['properties']['name']}, {round(feat['properties']['length'] / 1609, 1)} mi"
        feat["properties"]["tooltip"] = tooltip
    return G, nodes, edges