Castlecary has a very specific characteristic - or more accurately - its famous Arches do. They are an isogloss.
An isogloss, also called a heterogloss is the geographic boundary of a certain linguistic feature, such as the pronounciation of a vowel, the meaning of a word, or the use of some morphological or syntactic feature. Major dialects are typically demarcated by bundles of isoglosses, such as the Benrath line that distinguishes High German from the other West Germanic languages.
Along with the adjacent Forth and Clyde Canal and the Bonny Water, the viaduct acts as a physical representation of Castlecary's status as an isogloss, as it is around here that there is a distinct change from the West Central Scots accent spoken around Cumbernauld (many of the town's residents having strong links to Glasgow) to the East Central Scots spoken in nearby Bonnybridge and Denny. Around 15 miles (24 km) to the south-east, Harthill is another location alongside a motorway perceived to denote a shift between dialects as well as local authorities.
Cache is placed near the Antonine Wall - a more physical barrier across Central Scotland!