Over the centuries, the population growth led inhabitants to pass the second wall, when it existed, and to invade the nearest surroundings in a, at the beginning, moderate process, which was later accelerated by the effects of the industrial revolution.
Pablo Arias (2003), while revising urban history concludes that from the Roman city up to the eighteenth century, the formal and physical relationship of the city with its surroundings would remain relatively stable, with a closed city stated in the territory as the central fact and character, without altering the environment in which it was settled.
Traditional agricultural practices accelerated by new technologies, utensils and machinery depersonalized the previous relationship between towns and their territories. New tools formed part of the everyday landscape, and the result of their use, in many cases, homogenized the peripheral and rural landscape next to urban conglomerates.
Following the mentioned author, the difference between the ancient towns and the modern city, in terms of expansion, is the different behaviour in relation to its surroundings. The old historic towns reinforced their identity through the manner in which they were linked with the territory. Modern cities, on the other hand, exert the right to prey on the territory in searching of resources, some indispensable to live such as water and food, and some others necessary for social and economic development, such as roads and factories.
The confusion of this overwhelming texture of networks and frames depersonalized the old heritage sense of the city image in its territory; it is one of the most significant losses in the current city (Cano 1985)1
The city of Adelaide (Figure 3) represents an interesting example that illustrates a historical border that persists despite the later strong urban sprawl. Founded in 1836, the origins of this planned city have very little to do with walled towns, but the observed plan shape tells the story of a historical centre, a surrounding fringe and the later irregular sprawl. Adelaide was planned under Light  Vision, and the fringe – the Adelaide Parklands – that initially acted as the growth limit, contention and definition of the inside and the outside, now represents a great advantage. The needed green areas, usually desired when the population increases, were already there, bordering the old town. Although their general shape does not follow the Torrens river flow or other natural features that surely were there before the city construction, that green area represents an outstanding environmental and landscape resource that has a clear balancing effect.
Besides the environmental damage widely analysed under the concept of ecological foot print (Rees & Wackernagel 1994), the growth without borders or, better, without control, triggered by the conjunction of diverse forces that result in an invasive stain that spreads on the natural support to blot out all traces of what it was before.
Fig. 3. Adelaide, South Australia. Source: Google Earth 2012 2.3 Demographic explosion effect
Facing the need of expansion due to economic growth, cities used to be thought of in a centrifuge manner. The borders moved faster than the planning authorities attempted to solve or even understand problems. The growth had been predictable or at least reachable by remedial strategies for centuries, but the demographic explosion of the 60’s made an abrupt change on the previous inertia, mainly in the named "developing world". In this part of the earth, the situation has not just been severe because of the rapid urban rendering, expansion and consequent deterioration of places, but it has been aggravated by social unbalance, socio-political complex situations, and extreme environmental damage as well as consequent landscape disfigurement.
Facing the growth from this time onwards, planning authorities were at the beginning focused to solve issues from a single functional point of view, ordering and distributing land uses, as if the habitat were independent of inhabitants. That was the time of "zoning", a technical exercise that minimized the importance of the human behaviour of the diverse groups of population and communities and the significance of natural determinants of the territory.’
The evident dysfunction of that planning system and the increasing social set of problems drove planners attention to society; that is to say, to the collective human factor. Aspects such as education, health, the right to work, social security, among others became even more important than the assignation of uses to the land. In Colombia the beginnings of this kind of planning attitude could be placed in the 80’s decade, to be followed in the 90’s by the environmental worry.
Environmental issues have been much treated since the Stockholm Conference in 1972. But in the developing world it started to be important enough to be incorporated in local law two decades afterward. In general, the complex environmental problem seems to be increasing in a geometrical tendency, while the solutions increase in an arithmetical way.
Meanwhile, economical factors and land speculation go over the common sense of preserving resources and to treating them in a real sustainable manner. Words such as ecology, green, and sustainable, have lost their actual meaning and are used without measure. The "green wash" has invaded contemporary discourses hiding the real environmental question posed by the urban expansion.
To complete the spectrum, of zoning + social + environment, and rooted in its agglutinative and unifying role, many signals seem to point to this time being that when the integrator par excellence: THE LANDSCAPE occupies the deserved place as an important determinant in planning decision and purposes. As Sir Geoffrey Jellicoe thought The world is moving into a phase when landscape design may will be recognized as the most comprehensive of the arts (Jellicoe 1982).
To deal with the complex issue of indiscriminate urban expansion and moving peripheries a strategic coordination of many actors and factors is necessary. Of course the landscape design discipline is not enough but its contribution is indeed necessary first in helping to understand and balance the multiplicity of facets of the urban-rural border phenomena, and second to promote integrated answers to the complex trouble.