Getting the following error when I try and create a Folium - Choropleth map: ValueError: key_on `'id'` not found in GeoJSON

Question

ere's my code:

folium.Choropleth(

geo_data=geojson,

data=df,

columns=['Location ','Charging devices per 100,000 population'],

key_on='feature.id',

fill_color='YlGnBu',

fill_opacity=0.7,

line_opacity=0.2,

legend_name='Charging devices per 100,000 population'

).add_to(map1)

My Geojson file:

https://martinjc.github.io/UK-GeoJSON/json/eng/topo_lad.json

My Csv:

https://maps.dft.gov.uk/ev-charging-map/index.html

I renamed ONS to ID.

Please help.

Answer 1

• you are using topojson not geojson as your source geometry
• this means you need to also specify topojson parameter
• full solution is mostly dealing with fact that spreadsheet published by https://maps.dft.gov.uk/ev-charging-map/index.html mixes data dictionary and data together that requires clean up.
• a simpler alternative solution if you have it installed is with geopandas

full solution

import pandas as pd
import requests
import folium

# source data, requires https://pypi.org/project/odfpy/
df = pd.read_excel(
    "https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1048354/electric-vehicle-charging-device-statistics-january-2022.ods",
    engine="odf",
    sheet_name=1,
    header=[6, 7],
)

# cleanup description records...
df = df.loc[df.iloc[:, 0].str.match(r"^[A-Z][0-9]+").fillna(False)]

# reshape to much nicer shape..
df = (
    df.set_index(
        pd.MultiIndex.from_arrays(
            df.iloc[:, 0:2].T.values, names=df.columns.get_level_values(0)[0:2]
        )
    )
    .iloc[:, 2:]
    .stack(0)
    .reset_index()
).rename(columns={"level_2": "Date"})

# cleanup columns
df = df.rename(columns={c:c.strip() for c in df.columns})
df["Total devices"] = pd.to_numeric(df["Total devices"], errors="coerce")
df["per 100,000 population"] = pd.to_numeric(df["per 100,000 population"], errors="coerce")

# just most recent data
df = (
    df.sort_values(["LA / Region Code", "Date"])
    .groupby(["LA / Region Code"], as_index=False)
    .last()
)

geojson = requests.get(
    "https://martinjc.github.io/UK-GeoJSON/json/eng/topo_lad.json"
).json()

map1 = folium.Map(location=(52.83791067797496, -2.336002422471461), zoom_start=6, height=300, width=500)

folium.Choropleth(
    geo_data=geojson,
    topojson="objects.lad",
    data=df,
    columns=["LA / Region Code", "per 100,000 population"],
    key_on="feature.id",
    fill_color="YlGnBu",
    fill_opacity=0.7,
    line_opacity=0.2,
    legend_name="Charging devices per 100,000 population",
).add_to(map1)

map1

alternative

import geopandas as gpd

gdf = gpd.read_file("https://martinjc.github.io/UK-GeoJSON/json/eng/topo_lad.json").set_crs("epsg:4326").merge(
    df.drop(columns="Date"), left_on="id", right_on="LA / Region Code"
)


gdf.explore(column="per 100,000 population", cmap="YlGnBu", scheme="NaturalBreaks", height=300, width=500)