joined = {
const urbanRuralLookup = new Map(
designationUrbanRural.map(({ geoid, pct_rural_2010 }) => [
geoid,
pct_rural_2010 >= 50 ? "rural" : "urban"
])
);
return data.map((d) => {
const designation = urbanRuralLookup.get(d.fips);
return {
...d,
designation
};
});
}