import type { Datum } from "../charts/shared/datumTypes";
/**
 * Merge external data into GeoJSON features by joining on a key field.
 *
 * @example
 * ```ts
 * const enriched = mergeData(worldCountries, myCSV, {
 *   featureKey: "properties.iso_a3",
 *   dataKey: "country_code"
 * })
 * ```
 *
 * Cross-pollination: This pattern (key-based data join) could be extracted
 * to a shared utility for any data merge operation in Semiotic.
 */
export declare function mergeData<T extends Datum>(features: GeoJSON.Feature[], data: T[], options: {
    featureKey: string;
    dataKey: string;
}): GeoJSON.Feature[];
