图层
1、加载地图，选择图层 
  if(!Page.IsPostBack)
   {
    MapControl1.Map.Clear();
    MapControl1.Map.Load(MapLoader.CreateFromFile(Server.MapPath("/mymap")+"\\map\\xy.gst"));
    MapControl1.SelectableLayers.Clear();
    MapControl1.SelectableLayers.Add("o地名p");
   }
2、清空图层
可以把图层当成一个结果集
    (_tempTable as IFeatureCollection).Clear();
3、根据图层名获得图层
    MapInfo.Engine.Session.Current.Catalog.GetTable(TableName)

图元
1、遍历所有结果集
   Selection sl =MapInfo.Engine.Session.Current.Selections.DefaultSelection;
   IResultSetFeatureCollection fc=sl[0];
   IFeatureEnumerator fn=fc.GetFeatureEnumerator();
   ListBox1.Items.Clear();
   while(fn.MoveNext())
    if(fn.Current.Geometry.GetType().ToString()=="MapInfo.Geometry.LegacyText")
     ListBox1.Items.Add(((MapInfo.Geometry.LegacyText)fn.Current.Geometry).Caption);
2、根据关键字获得（第一个）图元
    MapInfo.Engine.Session.Current.Catalog.SearchForFeature("Layer1",MapInfo.Data.SearchInfoFactory.SearchWhere("MI_Key='"+strKey+"'") )