id: the geography to draw, e.g. 'us:county:34013'. children_level: draw everything at that level inside it
instead, e.g. every 'precinct' in a county or state, every 'county' in a state, every 'polling_division' in a
riding, or every 'precinct' overlapping a congressional district (any share; use related_geographies for shares).
detail: 'high' (~10 m), 'medium' (~50 m, default) or 'low' (~200 m). Neighbouring shapes from the same source
share identical edges at every detail level. clip_to_land: trim open water (ocean, bays, Great Lakes) using
the state/province shoreline outline (default true; inland lakes are not trimmed; shorelines are generalized
to ~1:500k, widened ~200 m so land isn't cut); false gives legal extents. include_districts: add each feature's
congressional / state senate / state house district holding the largest share of its population.
Feature properties: id, level, code, name, parent_id, region, population (2020 Census for precincts and towns,
latest estimate for counties and states), vintage and source_id (2020 Census VTDs have source_id
'us-census-vtd-2020'; current precincts don't), shape_source.

Small results come back inline as `geojson`. Larger ones are not returned inline (they'd flood the
conversation): the hosted service returns a short-lived `download_url` (fetch it with curl into your project);
a local server writes the file to its own export folder and returns `file` (copy it into your project). Page
big selections with offset/limit (max 5000 features).