Modern conceptions about nations and borders just did not exist in feudal Europe. Dukes and other feudal underlings held a significant amount of power, often to the point of full sovereignty, and often held territories under different kings and actively (and militarily) opposed their titular master. such as the case of the Duchy of Burgundy (which once upon a time was one of the most powerful actors in Europe), or the kings of England in their role as dukes of Normandy/Aquitaine.
Not even considering the situations where crown authority is so weak a central state can only be considered to exist in name alone such as the Byzantine empire at several stages in its existence, or the Holy Roman Empire
People back then, more often than not did not adhere to some national identity, usually identifying more with their local town/city/whatever. Their language and culture reflected this reality as well, such as in France and the case of the Langues d'oïl and the Langues d'oc.[2] The languages spoken in southern France were closer to what we now call Spanish or Italian dialects than northern dialects. Nationalism and national identity are very much a modern concept.
This map is pretty much just fluff for these reasons.
A fantastic take on these concepts is the game crusader kings II, which strives to recreate the accurate political realities of medieval Europe. It can be quite challenging to "get it" as a modern player, but it all clicks when you realize whats important is the success of your dynasty rather than your titular holdings (nation). Often related, but often quite opposed!
[1] http://en.wikipedia.org/wiki/Presentism_(literary_and_histor...