The county-level service area of Medicare Advantage contracts, month by month, from CMS's monthly MA Contract Service Area file (2006-10 on; 2022-11 was never published). Both directions: the counties a contract serves (contract_id) and the contracts serving a county (county_fips, 5 digits) or a state (state_code, 2 letters).

WINDOW: report_month (YYYY-MM) or year; with neither, the newest month held (stated in value.query.report_month).

RETURNS value.summary (distinct contracts, counties, contract-counties and contract-county-months; national, employer-group and partial-county counts; the months read), value.contracts (one row per contract: organization, organization type, plan type, counties served, employer-group and partial counties) and value.rows (one row per contract, county, month and flag combination: state_code, county_fips, county_ssa, county_name, eghp, partial_county, national_service_area). limit bounds both lists (default 100, max 2000); a truncated list carries a caveat.

THREE RULES: (1) eghp (employer-group only) and partial_county are CMS's own flags; eghp_only=true keeps employer-group rows. (2) A contract serving the whole country (National PACE and similar) is one national row with no state or county (national_service_area=true); it is never counted as a county, and a state or county filter leaves it out unless include_national=true. (3) CMS lists a contract-county twice when its plans there differ in the partial or employer flag, so count DISTINCT contract-counties, never rows; the summary already does.

Each month is read at its newest CMS edition. Stand-alone Part D (PDP) service areas are a separate file and are not here.