The Lex Frisionum, for instance, distinguishes three districts of Frisia, defining  West Frisia as the territory "between Zwin and Vlie" (present-day Holland and Zeeland) and East Frisia as the territory "between Lauwers and Weser".
The Lex Frisionum is a historical document that outlines the geographical divisions of Frisia. It specifically identifies West Frisia as the area between Zwin and Vlie (present-day Holland and Zeeland) and East Frisia as the territory situated between Lauwers and Weser.