Very interesting topic Paula and Massimo. In my opinion it´s necessary to change structurally our urban policy, and generate local partial plans to better regulation in our cities, in a more dynamic way that our current regulatory plans. Sad to say but there are many cities that has Agenda 21 but their growth is uncontrolled and as a result of property speculation (i.e. Valencia as paradigmatic case).

I agree that we need put the focus in the local administrative and political level, in city councils, but with smarts laws and more citizen control. The political decisions and their impact on changes to regulatory plans, in example.

I think that is where efforts should be focused. We should also generate assets other control mechanisms, such as urban observatories made ​​up of academics, legislators (well-informed) and citizenship and social organizations.

Paula, Leonardo, thank You for the answers... I have more questions...

In the Agenda 21 of Barcelona and Valencia, is a specifc point on vertical growth included? Is a hight limitation for new buildings established? I remember that in Barcelona midtown ("Eixample") the existing built environment fixed the hight of new buildings, but I don't know if in new neighboors similar norms are applied.

In Antofagasta (and in Chile in general), the only regulation is an angular relationshiop between the street large and the building hight.

The continuity of the first line in front to the Sea is also frecuently interrupted and there is no hight uniformity. What do You think about?

Perhaps the best first line of a city I ever seen is in Montevideo, that has one of the first masterplans in LatinAmerica.

Angular "limit" (high to width ratio) existed in Barcelona from some time. But, usually speculation and high rise are very difficult to "reverse". Any decision on urban plans first has to be done, then to consider that cycle of life is large for building's body (maybe 100 years at least for the body of the buildings (not the use)?) , then force to accomplish the rules (I remember a case near Barcelona, planned/allowed body of buildings sourrounding a park, then the built buildings had at least 1 floor more than allowed...)... it seems the "dynamics" is in the many, many years...

So, as summary: norms are needed, if given "no norms", urban spaces will evolve to mostly "chaotic" disordered and with many low quality space.

What would be the best norms, that's difficult, a conflict of interests, but in any case, much better that "no norms" as had been proved in china.

In any case, if "no norms" exist, there is the experience of Kowloon (look for it in the internet if you didn't knew), which shows an irregular, aparently hiperdense net, but a problematic built ensemble (also, higher density could be achieved if well planned, I think, but this is an opinion).

Interesting case... limited in vertical growt, but dense. Obviusly, it is not a best practice example, however it seems to me that the concept of block of this place could be used in a modern way. Security issues are also limiting this kind of urban structures, more than efficiency concepts...

Another important fact to consider is that the ability to green the city is made much harder the more vertical you go.

I have lived and worked in Hong Kong and am very familiar with the dense vertical Kowloon (that Antonia mentions). I also live and work in South Africa where the cities are low, open and sprawling horizontally.

My observations are that the quality of life in Hong Kong is actually lower than that in South Africa (despite the higher incomes, much lower crime-rates, and vastly superior transport system in HK). One of the reasons why South African cities are more enjoyable is the greenery, and clean air! People are still connected with Nature.

This connection and appreciation is generally lost in Hong Kong, especially in Kowloon. Sure, people can take trips out to the country parks on weekends, but how many HK city-folk are actively engaged in gardening themselves and living every day in their own gardens? Very Few. This environmental psychological aspect is underestimated in urban policy, in my opinion.

CONCLUSION: If one goes vertical and denser, it must be done so with a policy that densifies the greening of the city too.

Derek, good answer. I would ask you, as you lived in these very different cities, what do you think about the heat island effect? Some researchers sustain the idea of " the higer the sprawl, the higer the heat island effect", but I desagree... The main point of their idea is that more roofs absorb more heat, but in my opinion the albedo reduction of a dense city is more important than other considerations.

Massimo, I agree with you (I think).

Again, I think the argument is largely about greening, or more specifically the PROPORTIONS of greening to hard surfaces - not so much whether we go vertical or horizontal in our expansion.

Factors affecting the ‘Urban Heat Island Effect’ (UHIE) include:

1) the number of built structures with heat absorbing properties,

2) the reduction in evaporating surfaces (i.e. the lack of vegetation cover),

3) increased surface run-off (including the amount of road surfaces),

4) an increase in air pollutants,

5) heat production from buildings, and

6) less cooling wind because of shelter from buildings.

What exactly do you mean by "albedo reduction" of a dense city? To me, that depends largely on what buildings are made of, which is not straightforward; old or new buildings, shiny or matt surfaces, energy retention of materials (e.g. concrete vs metals), dust and grum collected on them, etc. If one looks at old Kowloon buildings they have many dark asphalt roofing materials (cheap) that absorb heat. The results are very obvious - the increase in temperatures at the Hong Kong Observatory (near Kowloon) is 0.6°C per decade, compared to the outlying areas of HK which generally matches global warming trends of around 0.2°C per decade.

Incidentally, other newer parts of HK might use special tiles or reflective white surfaces on their roofs. However, with tall buildings looking down these, glare from these surfaces becomes a new issue. Also, the maintenance of keeping a roof white enough to optimise its albedo value is actually much worse than one might think. Greening of the roofs is likely to be one good solution as it overcomes both of these new problems.

I suppose my answer is similar; the denser one go the worse urban heat island gets. This is GENERALLY the case, but not always, because the denser one goes the more greenery is sidelined (in my view). Cities like Singapore may be the exception where they have greened in proportion with their densification.

Unlike the figures I mentioned above for Hong Kong, I have no quotable measurements for the 'Urban Heat Island Effect' in South African cities, except my personal experience. Where the urban sprawl is residential people plant many trees - UHIE is minimal if anything. Where the sprawl is expansive shopping areas (that sometimes accompanies these residences), one can immediately feel the effect driving into those areas.

CONCLUSION: if one talks about sprawl causing UHIE one needs to be specific about the type of sprawl. If one talks about vertical development causing UHIE one also needs to be specific about the materials used and so on. Generally greening is the solution and this is still more easily done in horizontal cities than vertical ones.

Albedo depends on surface materials of buildings and soils, of course. The roofs are very important and sprawl increases the roof surface, but generally I think that a dense city has more matter and vertical surfaces also absorb sun heat and don't have high losses to sky (while roofs loose heat to sky). I agree with you respect to the greening, that would be the key factor to reduce heat island effect. Thank you again for the answer, very complete and interesting.

Yes, sprawl will have a high number of roofs per person, and roads too, but whether this is such a big issue when there is plenty of greenery is what needs to be argued.

Personally, I tend to think it is NOT such a big issue, and I also agree with you that generally dense cities have more hard surfaces that trap latent heat in them than sprawled-out cities.

I have said it previously but I think it comes down to a "PROPORTIONS game". Of equal importance is how the actual "urban fabric" is designed !

What I mean by that is the SCALE of how things are designed or how closely the greenery is INTEGRATED.

For example, if you look at Hong Kong, in general, it has plenty of greenery in its country parks to offset the amount of urban areas. Its proportions might appear correct. However, problem is that this greenery is not where it is needed, i.e. in the heart of the built-up areas where it would play a role in cleaning the air and shading the buildings, etc. The greenery needs to be up-close and integrated into the city and the buildings to be effective.

How to quantify all this could be an interesting research question. General proportions could be analysed quite easily with a GIS system. However, determining what "scale" or "integration" of greening is effective in a city (at reducing UHIE, cleaning the air, etc.) could be a lot more challenging.

https://www.researchgate.net/publication/230738894_Peri-Urban_to_Urban_Landscape_Patterns_Elucidation_through_Spatial_Metrics

https://www.researchgate.net/publication/229826816_Empirical_patterns_of_the_influence_of_Spatial_Resolution_of_Remote_Sensing_Data_on_Landscape_Metrics