How to get the bounding box (MultiPolygon) of a geographic region?

Question

I need to execute a BigQuery database query whereby I'm trying to ascertain if a given lat, lon coordinate is within one of a few US counties.

One of those counties is Collin County in Texas, shown here in Google Maps:

BigQuery supports GIS functions I'd need like ST_CONTAINS, but I can't figure out how to get, say, a GeoJSON representation of that polygon Google Maps is showing from either that service or OpenStreetMap.

The closest I've gotten with OpenStreetMap + Overpass is the following query:

[out:json][timeout:180];
relation(1837688);
out geom;

But the polygon I try to create from that response using members doesn't line up with what OpenStreetView has https://www.openstreetmap.org/relation/1837688.

Is there a more general solution I can use to create these bounding polygons for a region?

Answer 1

BigQuery has a few public datasets, including US counties, that you can directly use.

SELECT geo_id, state_fips_code, county_name, county_geom 
FROM `bigquery-public-data.geo_us_boundaries.counties` 
WHERE county_name LIKE '%Collin%'

This returns two counties, the one with geo_id = 48085 seems what you need. Here it is in BigQuery GeoViz: