Central Belt  "Not to be confused with the Central Lowlands, which includes this area." The Central Belt of Scotland is the area of highest population density within Scotland. Depending on the definition used, it has a population of between 2.4 and 4.2 million covering an area of approximately 10,000 km2, including Greater Glasgow, Ayrshire, Falkirk, Edinburgh, Lothian and Fife. Despite the name, it is not geographically central but is nevertheless at the "waist" of Scotland on a conventional map and the term "central" is used in many local government, police and NGO designations. It is likely considered the heart of the lowlands, a very old term and was for a few centuries sometimes recorded in Scotland as the Midlands and elsewhere as the Scottish Midlands which fell out of fashion. The Central Belt lies between the Highlands to the north and the Southern Uplands to the south. In the early 21st century, predictions were made that due to economic migration indicators, the urban areas of Glasgow and Edinburgh, whose centres are approximately apart, could merge to create a megalopolis over the coming decades. The area is often considered as the "triangle" defined by the M8, M80 and M9 motorways stretching from Greenock and Glasgow in the west to Edinburgh in the east, encompassing towns such as Paisley, Cambuslang, Hamilton, Stirling, Falkirk, Cumbernauld, Livingston and Bathgate. It has been referred to as the Lowland Triangle. The population of the local authority areas which are wholly within this territory and have no extensive unpopulated areas was approximately 2.39 million in 2018. The larger Central Belt is a trapezoid, not precisely defined, but essentially encompassing the generally low-lying areas from Helensburgh to Montrose (the Highland Boundary Fault) and from Girvan to Dunbar (the Southern Uplands Fault). This also takes in fairly densely populated regions such as Ayrshire and East Lothian, and encompasses all the major cities of Scotland, except for Aberdeen and Inverness which are located in the north of the country, as well as the bulk of Scotland's industrial works. Including rural parts of the council areas involved, the total population was around 4.28 million in 2018. There are several terms in common usage in a Scottish context with a similar meaning to "Central Belt".