.. This document is auto-generated by the altair-gallery extension. Do not modify directly.

.. _gallery_airports_count:


Locations of US Airports
========================
This is a layered geographic visualization that shows the positions of US
airports on a background of US states.


.. altair-plot::
    :code-below:

    
    import altair as alt
    from vega_datasets import data

    airports = data.airports.url
    states = alt.topo_feature(data.us_10m.url, feature='states')

    # US states background
    background = alt.Chart(states).mark_geoshape(
        fill='lightgray',
        stroke='white'
    ).properties(
        width=500,
        height=300
    ).project('albersUsa')

    # airport positions on background
    points = alt.Chart(airports).transform_aggregate(
        latitude='mean(latitude)',
        longitude='mean(longitude)',
        count='count()',
        groupby=['state']
    ).mark_circle().encode(
        longitude='longitude:Q',
        latitude='latitude:Q',
        size=alt.Size('count:Q', title='Number of Airports'),
        color=alt.value('steelblue'),
        tooltip=['state:N','count:Q']
    ).properties(
        title='Number of airports in US'
    )

    background + points


.. toctree::
   :hidden: