A sector like this is represented by a grid across a fairway (see the image above).
For example, search for ‘Maasbruggen’ and then tap ‘Reporting point Sector Maasbruggen Nieuwe Maas Oost’ in the search results. You will then see a VHF sign indicating the VHF channel of that sector. When you tap on such a VHF icon, you will see the name of such a sector: useful if you want to report to the shipping escort of such a sector.
At a structure (movable bridge, lock) when you tap the bridge or lock icon
For example, search for ‘Oostbrug’ in Rotterdam. If you tap that, you will see a VHF icon with ‘20’ behind it in the detail window that appears. See the image below.
