In many of the world's poorer countries, there are extensive slums or shanty towns, typically built on the edges of major cities and consisting almost entirely of self-constructed housing built without the landowner's permission. While these settlements may in time become upgraded, they often start off as squats with minimal basic infrastructure. Thus, there is no legal link to sewerage, electricity or water. Such settlements also exist in industrialized countries, such as for example Cañada Real on the outskirts of Madrid.