Create a polygon by clicking on a number of vertices in a closed path.
Try to get as many E1C0S3 point clusters (shown as black pins with a red shadow) inside it, while avoiding those that are far away.
You may view the latest public edit* for the E1C0S3 polygon here, or download the latest polygon dataset over here.
*The public edit which has more geocoded E1C0S3 points and fewer geocoded points for other postal codes inside, becomes the current default edit.