Altair choropleth map, color highlight based on line chart selection

Hi!

I am plotting a choropleth map colored by the field Passenger_0_ and a line chart showing the evolution of Passenger_0_ throughout a day by zone.

I would like to select a line (zone) in the line chart and have it highlighted in the map and vice versa (select a zone in the map and have it highlighted in the line chart).

For now, I am able to change the whole color of the map when selecting the line, but have no clue of how to only change the color of the selected area.

I would appreciate any help. This is the code:

dict_json = json.loads(long_df[long_df['hour']==0].to_json())

colours_obj = alt.Color('properties.Passenger_0_:Q',
              scale=alt.Scale(scheme='yelloworangered'),
             title = "Pickups")

sel_line_hover = alt.selection_single(on='mouseover', empty='none')
sel_line_col = alt.selection_single()
sel_line_size = alt.selection_single(empty='none')

base = alt.Chart(alt.Data(values=dict_json['features'])).mark_geoshape(
    stroke='black',
    strokeWidth=1
    ).encode(
    color=alt.condition(sel_line_col, colours_obj, alt.value('lightgray')),
    tooltip = ['properties.zone:O',
               'properties.Passenger_0_:Q']
    ).properties(
    width=350,
    height=750,
    ).add_selection(
    sel_line_col
    )

line = alt.Chart(long_df).mark_line().encode(
    x='hour',
    y='Passenger_0_',
    color=alt.condition(sel_line_hover|sel_line_col, 'zone', alt.value('lightgray')),
    size=alt.condition(sel_line_hover|sel_line_size, alt.value(4),alt.value(1)),
    tooltip = ['zone:O']
    ).properties(
    width=250,
    height=750,
    ).add_selection(
    sel_line_hover,sel_line_col,sel_line_size
    )

base | line

[angelrps]

Thank you very much for your answer @joelostblom I haven´t had time to try your solution but I will close this issue until I test it.

[joelostblom]

Answered on SO.. @angelrps if my reply there solves your problem, could you close this issue?