Hej Sybren,
Sybren is a spelling variant of Sibren, a Frisian form of the Old
German names Sigbern (victory + bear) and Sigbrand (victory + sword).
Here's a map of Friesland:
http://www.famato.de/frieslandlotse/friesland.gif
Westfriesland belongs to the Netherlands, Ostfriesland belongs to Germany and Nordfriesland to Germany and Denmark.
Regards,
Satu