I Fields pFields=new FieldsClass();
IFieldsEdit pFieldsEdit=(IFieldsEdit)pFields ;
IField pField=new FieldClass();
IFieldEdit pFieldEdit=(IFieldEdit)pField ;
pFieldEdit.Name ="Shape";
pFieldEdit.Type = ESRI.ArcGIS.Geodatabase.esriFieldType.esriFieldTypeGeometry;
IGeometryDef pGeomDef =new ESRI.ArcGIS.Geodatabase.GeometryDefClass();
IGeometryDefEdit pGeomDefEdit =(IGeometryDefEdit)pGeomDef;
pGeomDefEdit.GeometryType=ESRI.ArcGIS.Geometry.esriGeometryType.esriGeometryEnvelope; pFieldEdit.GeometryDef =pGeomDef ;
pFieldsEdit.AddField (pField);