I'm finding it difficult to believe that map relates to the title. It's not showing just the Scottish Highlands (roughly speaking the north-west half of Scotland), but the whole of Scotland, Ireland and Wales, plus about half of England, including the famously flat Lincolnshire fens.
So, you expected a map that omits all adjoining land to the mountains?
Most people wouldn't object to an article about Kilimanjaro containing a map of where it is in Tanzania, but for reference, here is a map of just the mountain: O.