Scotland
To the north and west of the Highland Boundary Fault are the more mountainous Scottish Highlands and islands, and this half of the country contains less than 5% of the total population.  To the south and east of the Highland Boundary Fault is the Scottish Lowlands, which contain the vast majority (about 75%) of the Scottish population, and 3 of the 4 biggest cities (Glasgow which is 1st, Edinburgh which is 2nd, and Dundee which is 4th).  Below the lowlands are the Southern Uplands which are hilly, but not as hilly at the Highlands.  They are less densely populated than the lowlands, but still a lot more dense than the highlands and islands.