Maps have a specific case where we can't migrate to node 10, see T213077: Migrate Kartotherian to node-mapnik >v4.2.1 to support libmapnik >3.1.x . Because of that, maps can't use the new package created on T203239: Create Debian packages for Node.js 10 upgrade.
Since there is no estimative for mapnik to release the needed version soon, it's desirable to migrate the maps services to node 8 before node 6 LTS ends.