Without wishing to get too involved in this discussion I would just like to point out that Highland clans actually began just north of Glasgow (Buchanan, Colquhoun, McGregor etc) then stretched northwards and westwards. As Glasgow is considered in the "Lowlands" you can see where confusion arises. Also large parts of the "Lowlands" were Gaelic-speaking (Ayrshire, Dumfries-shire) with strong Irish connections due to their proximity to Ireland.
The eastern borders of Scotland then up to Edinburgh, Perth and beyond to Aberdeen, the non-Gaelic speaking areas, are what you might think as the "Lowlands" and the borders, in particular have much in common with the northern counties of England. They even share similarities in place names such as the Scots spelling in Bamburgh, Dunstanburgh as distinct from the southern English "borough".