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From Territories, go to Maps, then Congregation Boundaries.
Your branch territory provides a KML file with your congregation's boundary. Download it from your hub.jw.org account, under Congregation Information and Territory, then click Download KML. If you don't have access to hub.jw.org, your secretary can provide the file. Import it here to set your boundary automatically instead of drawing it by hand.
This is the outer boundary of the whole congregation area, distinct from individual territory boundaries.
Territories > Maps > Congregation Boundaries