Text as tooltip, popup or labels in folium choropleth GeoJSON polygons

Question

Folium allow to create Markers with tooltip or popup text. I would like to do the same with my GeoJSON polygons.

My GeoJSON has a property called "name" (feature.properties.name -> let’s assume it is the name of each US state). I would like to be able to display this as a label in my choropleth map, in addition to the unemployment rate in each state. I also have the same information in the "State" column from the pandas dataframe.

Is this possible? I would be happy with a solution that allows this to be a popup, tooltip or a simple text label written on top.

import pandas as pd


url = (
    "https://raw.githubusercontent.com/python-visualization/folium/master/examples/data"
)
state_geo = f"{url}/us-states.json"
state_unemployment = f"{url}/US_Unemployment_Oct2012.csv"
state_data = pd.read_csv(state_unemployment)

m = folium.Map(location=[48, -102], zoom_start=3)

folium.Choropleth(
    geo_data=state_geo,
    name="choropleth",
    data=state_data,
    columns=["State", "Unemployment"],
    key_on="feature.id",
    fill_color="YlGn",
    fill_opacity=0.7,
    line_opacity=0.2,
    legend_name="Unemployment Rate (%)",
).add_to(m)

folium.LayerControl().add_to(m)

m

Asked By: G. Macia

||

Source

Answer 1

I’ve had to use folium’s GeoJsonTooltip() and some other steps to get this done in the past. I’m curious to know if someone has a better way

Capture the return value of the Choropleth function
Add a value(eg unemployment) to the Chorpleth’s underlying geojson obj
Create GeoJsonTooltip with that value from step 2
Add that tooltip to the choropleth’s geojson

url = (
      "https://raw.githubusercontent.com/python-visualization/folium/master/examples/data"
  )
  state_geo = f"{url}/us-states.json"
  state_unemployment = f"{url}/US_Unemployment_Oct2012.csv"
  state_data = pd.read_csv(state_unemployment)
  
  m = folium.Map(location=[48, -102], zoom_start=3)
  
  # capturing the return of folium.Choropleth()
  cp = folium.Choropleth(
      geo_data=state_geo,
      name="choropleth",
      data=state_data,
      columns=["State", "Unemployment"],
      key_on="feature.id",
      fill_color="YlGn",
      fill_opacity=0.7,
      line_opacity=0.2,
      legend_name="Unemployment Rate (%)",
  ).add_to(m)
  
  # creating a state indexed version of the dataframe so we can lookup values
  state_data_indexed = state_data.set_index('State')
  
  # looping thru the geojson object and adding a new property(unemployment)
  # and assigning a value from our dataframe
  for s in cp.geojson.data['features']:
      s['properties']['unemployment'] = state_data_indexed.loc[s['id'], 'Unemployment']
  
  # and finally adding a tooltip/hover to the choropleth's geojson
  folium.GeoJsonTooltip(['name', 'unemployment']).add_to(cp.geojson)
  
  folium.LayerControl().add_to(m)
  
  m

Answered By: Bob Haffner

Answer 2

Bob’s solution works well. Two notes:

For this to work, you need to have values in the data table (here: groupValues) for all the entries in the geo_data= table (here: counties) specified in the folium.Choropleth definition.

cp = folium.Choropleth(
        geo_data = counties,
        name = 'choropleth',
        data = groupValues, 
etc.

If an entry in the geo_data table lacks a corresponding value in data table, the loop will throw a KeyError. To fix this, I created a loop that uses try . . . except to add the correct values to the geojson table.

I was able to add numerical data (float64) to the cp.geojson table and folium allowed me to add it with the GeoJsonTooltip and LayerControl, but when I tried to display the map, I got an "float64 data cannot be serialized" error. I fixed this by converting it to a string before adding it to the cp.geojson table.

The working loop looks like this:

for row in cp.geojson.data['features']:
    try:
        row['properties']['PctAllPop'] = str(groupValues.loc[row['properties']['FIPS'],'PctAllPop'])
    except KeyError:
        row['properties']['PctAllPop'] = 'No adherents'
    
folium.GeoJsonTooltip(['NAME','PctAllPop'],aliases=['County:','Pct total pop:']).add_to(cp.geojson)

Answered By: Feikname

Text as tooltip, popup or labels in folium choropleth GeoJSON polygons

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