To support shipping rules based on geographic polygons, an interface extension on the WebStore Manager. When specifying rules, by choosing Shipping Address Geo-coordinates you can input the area (polygon) to which the rule applies, in the form of a list of geo-coordinates.
You can then decide whether that geographic polygon is allowed or disallowed for the shipping method to which the rule applies.
You can see an example of such a rule here:
The coordinates are specified as longitudinal/latitudinal pairs, one per line, separated by commas. For example: