From 1500 on, Scotland was commonly divided by language into two groups of people, Gaelic-speaking "Highlanders" (the language formerly called Scottis by English speakers and known by many Lowlanders in the 18th century as "Erse") and the Inglis-speaking "Lowlanders" (a language later to be called Scots). However, movement between the two regions increased over the last few centuries. Highlanders moved to major cities (e.g. Glasgow and Edinburgh) and regions bordering the southern Highlands (e.g. Lowland Stirlingshire and Perthshire). This is evidenced by people with traditional Gaelic surnames (including anglicised varieties) currently living in these areas. Lowlanders also settled in Highland regions such as Moray, which was traditionally Gaelic-speaking but replaced with Doric in the 19th century. https://en.wikipedia.org/wiki/Scottish_people

Most commonly spoken in the Scottish Lowlands, the Northern Isles of Scotland, and northern Ulster in Ireland (where the local dialect is known as Ulster Scots), it is sometimes called Lowland Scots, to distinguish it from Scottish Gaelic, the Celtic language that was historically restricted to most of the Scottish Highlands, the Hebrides, and Galloway after the sixteenth century;[13] or Broad Scots, to distinguish it from Scottish Standard English. Many Scottish people's speech exists on a dialect continuum ranging between Broad Scots and Standard English. https://en.wikipedia.org/wiki/Scots_language

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Ah yeah sorry read "celtics" instead of gaels