How to use and block a specific color for a location in plotly chloropeth map (python)

Question

I'm trying to set a map of European country with their result in Eurovision. I have a button to choose the different countries ( Italy, France, Portugal, UK , etc ...)

For Example, if I choose to see the Result of Sweden, I want to see on the map the numbers of points given by the others according to a color scale. I success to do it !

But I want to visualize Sweden, for example in black on the map, to better see where it is, and the "neighborhood effect of notation" .

fig3 = go.Figure(data=go.Choropleth(
    locations=Euro_tr['Country_code'], # Spatial coordinates
    z = Euro_tr['Italy'], # Data to be color-coded
    locationmode = "ISO-3",
    colorbar_title = "Points donnés",
    text=Euro_tr['Country'],
   ))


fig3.update_layout(
    title_text = 'Score Eurovision',
    margin={"r":55,"t":55,"l":55,"b":55},
    height=500,
    geo_scope="europe" ,
 
    
)

#Make a button for each country
button=[]
for country in Euro_tr.columns[1:-1] :
    dico=dict (
                    label=country,
                    method="update",
                    args = [{'z': [ Euro_tr[country] ] }],)
    button.append(dico)

fig3.update_layout(
     updatemenus=[
        dict(
            buttons=button,
            
            
            
         y=0.9,
         x=0,
         xanchor='right',
         yanchor='top',
         active=0,
    ),
        ])

As you see in this example showing the points given to Sweden, I want Sweden to be in a specific color, independently to others countries, the ones that have given points and the ones that have given no points.

Thanks for your help !

Answer 1

I followed the answers from @vestland, and I succeed to put my country of interest in one color , independently to others by using fig.add_traces(go.Choropleth)

To have the possibility to change the data and the trace according to my country of interest, I use streamlit and buttons.

import streamlit as st
import pandas as pd
import numpy as np
import plotly.express as px
import plotly.graph_objects as go 

# Creation of graphes for each country 
Graphes=[]
for country in Euro_tr.columns[1:-1] : #To pass each country 

    Graphe=go.Figure(data=go.Choropleth(
    locations=Euro_tr['Country_code'], # Spatial coordinates
    z = Euro_tr[country], # Data to be color-coded
    locationmode = "ISO-3",
    colorbar_title = "Points donnés",
    autocolorscale= False,
    colorscale="viridis",
    text=Euro_tr['Country'],
   ))
    
    # customisation : title according to the country and its points
    Graphe.update_layout(
    title_text = "Total :Points donnés à {fcountry} qui a remporté {fpoints} points".format(fcountry = country, fpoints = Eurovision_tot['Result_tot'][Eurovision_tot["Country"]==country].values[0]),
    margin={"r":55,"t":55,"l":55,"b":55},
    height=500,
    )
 )
    # block a specific zoom on the map ( scope "europe" isn't complete for eurovision countries xD!)
    Graphe.update_geos(
    center=dict(lon= 23, lat= 54),
    lataxis_range=[31.0529,-40.4296], lonaxis_range=[-24, 88.2421],
    projection_scale=3
    )
    
    # add trace for the specific country.
    Graphe.add_traces(go.Choropleth(locations=Country_df['Country_code'][Country_df["Country"]==country],
                            z = [1],
                            colorscale = [[0, col_swe],[1, col_swe]],
                            colorbar=None,
                            showscale = False))
    
    Graphes.append(Graphe)

#creation selectbox to select country
col12, col22 = st.beta_columns([0.2,0.8])   # I use columns to put the selector on a  side and the graph on other side 
Pays=list(Euro_tr.columns[1:-1]) # List containing country's name
Selection_Pays = col12.selectbox('',(Pays)) #create a multiple selector with the different countries as possible choice


# define action according to the selection.
for country in Pays :
        if Selection_Pays== country : #if country is selected
            col22.plotly_chart(Graphes[Pays.index(country)]) # plot the corresponding map.

Answer 2

Even though you've built your choropleth map using px.express you can always add a trace using plotly.graph_objects with fig.add_traces(go.Choropleth) such as this:

col_swe = 'Black'
fig.add_traces(go.Choropleth(locations=df_swe['iso_alpha'],
                            z = [1],
                            colorscale = [[0, col_swe],[1, col_swe]],
                            colorbar=None,
                            showscale = False)
              )

To my knowledge it's not possible to define a single color for a single country directly, and thats why I've assigned z=[1] as a value, and a custom scale colorscale = [[0, col_swe],[1, col_swe]] to make sure that Sweden always is illustrated in 'Black'.

Code:

import plotly.express as px
import plotly.graph_objects as go

df = px.data.gapminder().query("year==2007")
fig = px.choropleth(df, locations="iso_alpha",
                    color="lifeExp", # lifeExp is a column of gapminder
                    hover_name="country", # column to add to hover information
                    color_continuous_scale=px.colors.sequential.Plasma)

df_swe = df[df['country']=='Sweden']
col_swe = 'Black'

fig.add_traces(go.Choropleth(locations=df_swe['iso_alpha'],
                            z = [1],
                            colorscale = [[0, col_swe],[1, col_swe]],
                            colorbar=None,
                            showscale = False)
              )

f = fig.full_figure_for_development(warn=False)

fig.show()