title: Create GeoJSON GraphQL schema from third party library
body: <p>I'm trying to use the <a href="https://github.com/ghengeveld/graphql-geojson" rel="nofollow noreferrer">graphql-geojson</a> library in an Apollo/Express app to serve GeoJSON responses. </p>
  
  <p>The library provides the resolvers but I haven't found a way to add the types to my schema definition without writing them out by hand. And even then that hasn't proven that simple.</p>
  
  <p>Another custom type, Date from <a href="https://www.npmjs.com/package/graphql-date" rel="nofollow noreferrer">graphql-date</a>, I can just declare in the schema as a custom scalar:</p>
  
  <pre><code>const typeDefs: DocumentNode = gql`
    scalar Date
    scalar PointObject
  
    type Station {
      id: ID!
      name: String!
      geom: PointObject
      created: Date!
    }
    ...
  }
  </code></pre>
  
  <p>However, declaring PointObject as scalar allows you to get the full GeoJSON (which is OK) but results in errors:</p>
  
  <blockquote>
    <p>"GraphQLError: Field \"geom\" must not have a selection since type \"GeoJSONPoint\" has no subfields."</p>
  </blockquote>
  
  <p>when you try to return a sub-selection of <code>geom</code>, e.g.:</p>
  
  <pre><code>{
    stations {
      id
      name
      geom {
        coordinates
      }
    }
  }
  </code></pre>
  
  <p>Is there a way merge the types provided by the library with my schema? </p>