Go to Settings > Delivery Zones and click Create zone above the map. Use the polygon tool to click points on the map and trace your area, then click back on your first point to close the shape. Give the zone a title and pick a route colour, then save. Once created, enable the Delivery zones Route Option to limit a route to orders inside that zone. Available in both EasyRoutes for Shopify and EasyRoutes for Web.
See: Delivery Zones