Short answers, pulled from the story.
A single line drawn from Stonehaven to Helensburgh on the Firth of Clyde separates two distinct worlds within Scotland. This boundary defines where the Lowlands end and the Highlands begin for most cultural purposes.
Coal mining has declined ever since the early 20th century ended its peak dominance. During the 19th century coal deposits drove significant industrialisation and urbanisation across this valley.
Before 1921 three counties held different names than they do now. East Lothian was Haddingtonshire while Midlothian carried the title Edinburghshire and West Lothian was known as Linlithgowshire during that earlier era.
The basins of the Rivers Forth and Clyde hold approximately 3.5 million people within the Central Belt. This area houses about 80 percent of Scotland's total population despite its small geographic footprint.
Scottish Gaelic was historically spoken in the lowlands until the 15th century in many areas yet Galloway retained Gaelic speech until the 18th century despite being geographically within the Lowlands.