A Typescript interface for GeoJSON objects based on rfc7946

geo-json.ts

export interface IGeometry {
    type: string;
    coordinates: number[];
}

export interface IGeoJson {
    type: string;
    geometry: IGeometry;
    bbox?: number[];
    properties?: any;
}


export class GeoJson implements IGeoJson {
  constructor(public type, public geometry, properties?, bbox?) {}
}

You can use a union type, which will allow either a number[] or a number[][].

{
  // ...
  coordinates: number[] | number [][];
}

Yes, but in case the feature type is MultiPolygon then coordinates must be:

{
  // ...
  coordinates: [number, number][] | [number, number][][] | [number, number][][][];
}

and since the coordinates are always a two element tuple it is better to describe as [number, number] instead of number[]