Westergoa was one of the Seven Sealands and one of the three that now lie within the borders of today's Dutch province of Friesland.
In the Middle Ages Westergoa most probably formed the political centre of the Frisian realm.
On the south side it bordered with what originally was Bornegoa which was in the line with Terhernster Lake to the south of the coast, the eastern perimeter was with Doedingwerstal.
Also eight cities grew exceptionally in the Westergoa area; Harlingen and Franeker in the Fiefdielen part, Bolsward at the eastern side of Wildinge, now Wûnseradiel and at the southern point Workum and Hindeloopen.
Stavoren, Sneek and IJlst had become autonomous cities but six Frisian slots formed the grietenijen of Wymbritseradeel and Hemelumer Oldeferd (and Noardwâlde).