A useful starting point for the study of the surface of Italy is a consideration of three main types of relief: mountain, hill and plain. Fig. 2.1 shows the distribution of these elements, the definition of which is based broadly on altitude, the mountain areas being mainly above 1,000 metres, though containing many valleys below this level, the plains consisting of level or gently sloping land below about 300 metres, whether coastal or interior, and the hill country comprising the intermediate areas. The land classified as plain (pianura) occupies a little over one-fifth of the total surface of Italy while hill country (collina) accounts for over two-fifths and the mountain country (montagna) for somewhat less than two-fifths.
Although the basis for the division into three main types of relief is altitude, both relative relief and slope conditions are broadly related to altitude. In the mountain regions relative relief is greatest, reaching as much as 3,000 metres between valley floors and adjoining mountain summits in the Alps, and 2,000 metres in the highest parts of the Apennines. In the hill country it may reach several hundred metres in places. The mountain areas, too, tend to be the most rugged, having the steepest slopes, though gently sloping areas do of course occur. Much of the hill country is however also greatly dissected and is characterised by steep slopes, even though relative relief is not great; on the other hand, some hill country consists of gently sloping low plateaux. In the plains, naturally, slopes are generally gentle and relative relief slight.
The Alps, the Apennines and the mountains of Sicily form an almost continuous belt of mountain country of varying width, extending in the form of an S some 1,300 miles in length from the extreme north-east of Italy, first west, then curving round to Liguria and extending south-east and then south through the Peninsula and finally running from east to west across northern Sicily. There are other small mountain areas both in the Peninsula detached from the main range of the Apennines as in Tuscany, and in the island of Sardinia.
Italy has only one large area of plain, the North Italian Lowland, which lies between the Alps and the Northern Apennines, but there are many smaller plains in the Peninsula and Islands, some at or little above sea level along the coasts, others at a considerable altitude, forming small interior basins.
Almost everywhere hill country intervenes between the mountains and the plains, as around the North Italian Lowland, and between the mountains and the coast, as in the Peninsula and Islands. The most extensive areas of hill are in Central Italy but like both mountain and plain this form of relief occurs in almost every region. In almost any sizable part of Italy, indeed, a bewildering variety of relief conditions may be found, but a contrast between the North and the Peninsula should be noted. In the North, a series of roughly north-south sections shows the same general sequence of mountain-hill-plain-hill-mountain. On the other hand, roughly south-west-north-east sections across the Peninsula, while almost invariably crossing some mountain and hill and usually some plain, differ appreciably in the arrangement of these elements at different places along the Peninsula.
Italy has been divided into complicated physiographic regions by more than one geographer and it should be appreciated that no single system of regions satisfies everyone, since the result depends on the emphasis given to such varying criteria as altitude, age of rock, type of rock or predominant type of land form. For example, a convenient break in altitude in the Apennines, separating two high mountain areas, does not necessarily coincide with a geological or structural change.
