ArcMap 最上位レイヤーの取得

'ThisDocumentの取得
Dim pMxDocument As IMxDocument
Set pMxDocument = ThisDocument

'アクティブなデータフレームの取得
Dim pMap As IMap
Set pMap = pMxDocument.FocusMap

'最上位レイヤの取得
Dim pLayer As ILayer
Set pLayer = pMap.Layer(0)