The Hebrides consist of 

Outer Hebrides 

The main islands are allocated the IOTA  (Islands On The Air)  number EU-010,  the surrounding outlier islands being St. Kilda EU-059,  Monach Islands EU-111,  Shiant Islands EU-112,  Flannan Islands EU-118 ,  Rockall EU-189.
The islands are spread over a vast area from remote Rona in the north to Berneray in the south, about 175 miles,  the most westerly being the islet of Rockall 188 miles west of St Kilda.

Inner Hebrides
Also spread over a large area from Fladda-chuain near
Skye in the north to Islay in the south is 150 miles.

The main islands here are allocated IOTA number EU-008 with the Treshinish Islands being EU-108.