Basemap support for static and interactive geoshape charts

[gregorhd]

I saw the discussion in Vega-Lite issue #5758 regarding basemap support, which seems to be working even for interactive plots, but how would one implement this directly in Altair with a chart containing geoshapes?

On the static front, I got this chart to work based on a GeoPandas dataframe.

import geopandas as gpd
import altair as  alt
import altair_viewer
import json

gdf = gpd.GeoDataFrame(etc. etc.)

gdf_json = gdf.to_json()

json_features = json.loads(merged_json)

features = alt.Data(values=json_features['features'])

domain = ['Label1', 'Label2', 'Label3']
range_ = ['red', 'grey', 'cornflowerblue']

chart = alt.Chart(features).mark_geoshape().properties(
        projection={'type': 'mercator'},
        width=700,
        height=400
).encode(
        color=alt.Color("properties.Legend:N", scale=alt.Scale(domain=domain, range=range_), legend=alt.Legend(title='Legend', orient='top-right'))
    )

altair_viewer.display(chart)

Adding .interactive(), I faced the same problem as this user in issue #933, which according to the referenced issue #679 is due to vega-lite not, at least at that time, supporting geoshapes for interactive mode. Vega-Lite issue #5758 though would suggest that this is not current anymore, meaning one could even have an interactive geoshapes chart with a basemap?

Any pointers are much appreciated!

[jakevdp]

I don't think vega-lite has any support for scale-bound selections in geographic plots, which is what .interactive() attempts to add. So no, that is not supported in Altair.

[gregorhd]

Thanks, Jake! Does that mean tile basemaps for non-interactive charts are also not supported yet?

[jakevdp]

I don't know of any example of using basemaps in Altair, though for a motivated enough user it may be possible using something along the lines of the example in the linked vega issue.

[mattijn]

The example (Vega Editor) is based on VL5 features (params/expr) and is still not yet passing VL5.1-schema completely. Therefor I don't think this can currently be done in Altair. But the future is bright🙏

[gregorhd]

Thanks both! That's encouraging. I'll keep watching this space :)