In [ ]:
import altair as alt
from vega_datasets import data
import panel as pn

pn.extension('vega')

A simple example demonstrating how to use a reactive function depending on a single widget, to render Altair/Vega plots. In this case the Select widget allows selecting between various quantities that can be plotted on a choropleth map.

In [ ]:
altair_logo = 'https://altair-viz.github.io/_static/altair-logo-light.png'
states = alt.topo_feature(data.us_10m.url, 'states')
states['url'] = 'https://raw.githubusercontent.com/vega/vega/master/docs/data/us-10m.json'
source = 'https://raw.githubusercontent.com/vega/vega/master/docs/data/population_engineers_hurricanes.csv'
variable_list = ['population', 'engineers', 'hurricanes']

def get_map(variable):
    return alt.Chart(states).mark_geoshape().encode(
        alt.Color(variable, type='quantitative')
    ).transform_lookup(
        lookup='id',
        from_=alt.LookupData(source, 'id', [variable])
    ).properties(
        width="container",
        height=300,
    ).project(
        type='albersUsa'
    ).repeat(
        row=[variable]
    )

variable = pn.widgets.Select(options=variable_list, name='Variable', width=250)
logo = pn.panel(altair_logo, height=150, align="center")
vega_panel = pn.pane.Vega(sizing_mode="stretch_width", margin=(10,100,10,5))
    
@pn.depends(variable.param.value, watch=True)
def update_vega_pane(variable):
    vega_panel.object = get_map(variable)

update_vega_pane(variable.value)
    
pn.Row(
    pn.Column('# Altair Choropleth Maps', logo, variable),
    vega_panel
)

App

Lets wrap it into nice template that can be served via panel serve altair_chropleth.ipynb

In [ ]:
pn.template.FastListTemplate(
    site="Panel", 
    title="Altair Choropleth Maps", 
    sidebar=[logo, variable], 
    main=["A simple example demonstrating **how to use a *reactive function* depending on a single widget**, to render Altair/Vega plots.", vega_panel]
).servable();