Groupings by compass directions are the hardest to define in Europe, since (among other issues) the pure geographical criteria of "east" and "west" are often confused with the political meaning these words acquired during the Cold War era. For more details on this matter, see the articles on the following:
Describing the concentration of the wealth/economic productivity of Europe in a banana-shaped band running from London, through Benelux, eastern France, western Germany to northern Italy.