Is there anyway to popping out of part of Map or change of color on selection in Altair

Question

I am trying to plot the states of India in altair.I am able to plot and in the tooltip state names are appearing.I want the state to pop out or change in color on selection.Is there any way to do it.

I tried to use selection_interval.But not able to do it as i am newbie

'''python

import altair as alt

url = "https://raw.githubusercontent.com/deldersveld/topojson/master/countries/india/india-states.json"

source = alt.topo_feature(url, "IND_adm1")

alt.Chart(source).mark_geoshape().encode(
    tooltip='properties.NAME_1:N',
    color=alt.value('lightgray')   

).properties(
        width=800,
        height=500

)

Answer 1

You can use a Single Selection with a conditional color to do something like this:

import altair as alt

url = "https://raw.githubusercontent.com/deldersveld/topojson/master/countries/india/india-states.json"

source = alt.topo_feature(url, "IND_adm1")
hover = alt.selection_single(on='mouseover', empty='none')

alt.Chart(source).mark_geoshape().encode(
    tooltip='properties.NAME_1:N',
    color=alt.condition(hover, alt.value('steelblue'), alt.value('lightgray'))
).properties(
    width=800,
    height=500
).add_selection(
    hover
)