public ValueTuple<GeometryType,SpatialReference> GetShapeDefinition()

{
  await QueuedTask.Run(() =>
  {
    using (var kg = GetKnowledgeGraph(url))
    {
      var entity_name = "PhoneCall";
      var relate_name = "WhoCalledWho";

      var kvp_entity = kg.GetDataModel().GetEntityTypes()
           .First(r => r.Key == entity_name);
      var kvp_relate = kg.GetDataModel().GetRelationshipTypes()
                     .First(r => r.Key == relate_name);

      //Let's delete one field and add a new one from each
      //A field gets deleted implicitly if it is not included in the list of
      //fields - or "properties" in this case....so we will remove the last
      //property from the list
      var entity_props = kvp_entity.Value.GetProperties().Reverse().Skip(1).Reverse();
      var prop_descs = new List<KnowledgeGraphPropertyDescription>();

      foreach (var prop in entity_props)
      {
        if (prop.FieldType == FieldType.Geometry)
        {
          continue;//skip shape
        }
        var prop_desc = new KnowledgeGraphPropertyDescription(prop);
        prop_descs.Add(prop_desc);
      }
      //deal with shape - we need to keep it
      //SchemaBuilder deletes any field not included in the "modify" list
      ShapeDescription shape_desc = null;
      if (kvp_entity.Value.GetIsSpatial())
      {
        var geom_def = kvp_entity.Value.GetShapeDefinition();
        var shape_name = kvp_entity.Value.GetShapeField();
        shape_desc = new ShapeDescription(
          shape_name, geom_def.geometryType, geom_def.sr);
      }
      //add the new entity property
      prop_descs.Add(
        KnowledgeGraphPropertyDescription.CreateStringProperty("foo", 10));
      //make a description for the entity type - ok if shape_desc is null
      var entityDesc = new KnowledgeGraphEntityTypeDescription(
        entity_name, prop_descs, shape_desc);

      //Add the entity type description to the schema builder using 'Modify'
      SchemaBuilder sb = new(kg);
      sb.Modify(entityDesc);

      //Repeat for the relationship - assuming we have at least one custom attribute field
      //that can be deleted on our relationship schema...
      var rel_props = kvp_relate.Value.GetProperties().Reverse().Skip(1).Reverse();
      var rel_prop_descs = new List<KnowledgeGraphPropertyDescription>();

      foreach (var prop in rel_props)
      {
        if (prop.FieldType == FieldType.Geometry)
        {
          continue;//skip shape
        }
        var prop_desc = new KnowledgeGraphPropertyDescription(prop);
        rel_prop_descs.Add(prop_desc);
      }
      //deal with shape - we need to keep it
      //SchemaBuilder deletes any field not included in the "modify" list
      ShapeDescription shape_desc_rel = null;
      if (kvp_relate.Value.GetIsSpatial())
      {
        var geom_def = kvp_relate.Value.GetShapeDefinition();
        var shape_name = kvp_relate.Value.GetShapeField();
        shape_desc_rel = new ShapeDescription(
          shape_name, geom_def.geometryType, geom_def.sr);
      }
      //add a new relationship property
      rel_prop_descs.Add(
        KnowledgeGraphPropertyDescription.CreateStringProperty("bar", 10));
      //make a description for the relationship type - ok if shape_desc is null
      var relDesc = new KnowledgeGraphRelationshipTypeDescription(
        relate_name, rel_prop_descs, shape_desc_rel);

      //Add the relationship type description to the schema builder using 'Modify'
      sb.Modify(relDesc);

      //Run the schema builder
      try
      {
        //Use the KnowledgeGraph extension method 'ApplySchemaEdits(...)'
        //to refresh the Pro UI
        if (!kg.ApplySchemaEdits(sb))
        {
          var err_msg = string.Join(",", sb.ErrorMessages.ToArray());
          System.Diagnostics.Debug.WriteLine($"Entity/Relate Modify error: {err_msg}");
        }
      }
      catch (Exception ex)
      {
        System.Diagnostics.Debug.WriteLine(ex.ToString());
      }
    }
  });
}