getSelection() {
        const trackedObject = this.trackedObject;

        if (isVehicle(trackedObject)) {
            return trackedObject.object.id;
        } else if (isStation(trackedObject)) {
            return trackedObject.stations;
        }
    }
Returns the ID of the train or flight being tracked, or the IDs of the selected
stations.
@returns {string | Array<string>} The ID of the train or flight being tracked, or
    the IDs of the selected stations