Plotting Linestrings with a Colomap - Geopandas and Folium

Question

I have a geopandas data frame containing ~500 linestring and a column named total containing a number between 0 and 1.

I want to plot the linestrings on a folium map with a color that depends on the value of total. Thus, I defined a colormap as follows:

colormap = cm.LinearColormap(colors=['lightblue','blue'])

and I am plotting everything with the following code:

m = folium.Map(zoom_start=10, tiles='CartoDB positron')

for _, r in gdf.iterrows():
    geo_j = gpd.GeoSeries(r['geometry']).to_json()
    geo_j = folium.GeoJson(data=geo_j,
                           style_function=lambda x:
                                      {'lineColor':colormap(r['total']),
                                       'color': colormap(r['total']),
                                       'fill':True,
                                       'opacity': 1, 
                                       'fillColor': colormap(r['total'])})
    geo_j.add_to(m)

I tried with all the combinations of linecolor, color, fillcolor, opacity and whatsoever but all the lines are always plotted with the same color even if colormap(r['total'] works correctly (always different rgb are retrieved):

can anyone help?

Answer 1

• no sample data so have generated LineString between pairs of London Underground stations
• it's very simple to use https://geopandas.org/en/v0.10.0/docs/user_guide/interactive_mapping.html
• have demonstrated with generated sample data

import requests
import geopandas as gpd
import plotly.graph_objects as go
import itertools
import numpy as np
import pandas as pd
import shapely.geometry

# get geometry of london underground stations
gdf = gpd.GeoDataFrame.from_features(
    requests.get(
        "https://raw.githubusercontent.com/oobrien/vis/master/tube/data/tfl_stations.json"
    ).json()
)

# limit to zone 1 and stations that have larger number of lines going through them
gdf = (
    gdf.loc[gdf["zone"].isin(["1", "2"]) & gdf["lines"].apply(len).gt(2)]
    .reset_index(drop=True)
    .rename(columns={"id": "tfl_id", "name": "id"})
)

# wanna join all valid combinations of stations...
combis = np.array(list(itertools.combinations(gdf.index, 2)))

# generate dataframe of all combinations of stations
gdf_c = (
    gdf.loc[combis[:, 0], ["geometry", "id"]]
    .assign(right=combis[:, 1])
    .merge(
        gdf.loc[:, ["geometry", "id"]],
        left_on="right",
        right_index=True,
        suffixes=("_start_station", "_end_station"),
    )
)

# generate linestrings between stations
gdf = gpd.GeoDataFrame(
    geometry=gdf_c.select_dtypes("geometry").apply(shapely.geometry.LineString, axis=1),
    data=gdf_c,
    crs="EPSG:4326",
)
gdf["total"] = np.random.uniform(0, 1, len(gdf))

# now use explore that uses folium
gdf.explore("total", cmap="Blues", tiles="CartoDB positron")