This year, at the Architecture Biennale in Venice, Patrik Schumacher gave a fascinating introduction to the concept of ‘parametricism’ as a new style, that could be applied to all design tasks including urbanism. As creators of parametric city design software, we feel this is a good time to produce a quick summary of what parametric design is, and to share our view about its possibilities and limitations in the field of city design.
What is parametric design?
Parametric design is an established concept in CAD.
Instead of drawing lines, a design is created by specifying parameters, and the actual geometry is then generated automatically by the software.
In the diagram below, the line on the left is just a line – it is drawn from one end point to another. The street designs to the right, however, were drawn parametrically. The positions of the end points were specified and the software then generated the pavements, vehicle lanes, central reservations and trees based on pre-set parameters.
The parameters in this case are the number, type and width of the elements of the streetscape - the pavements, cycle lanes, trees, vehicle lanes and central reservation, and their relationship to each other.
‘Parametric’ simply means ‘of or relating to a parameter’ - or in the case of CAD, generated by parameters.
What are the benefits of parametric design?
In architectural design and engineering, parametric modelling tools allow designers to create a framework of relationships and constraints between parts of a model. If one part is adjusted, then other parts will be updated automatically according to pre-defined rules.
In the example of the streets above, you could type in a new width for the pavement, and the model will be updated automatically.
The advantages are clear – things can be drawn faster, more accurately and with less chance of mistakes, and they can be modified extremely quickly. They can also be used to automatically extract data such as floor areas, or quantities of materials.
The disadvantages are that the designer is constrained by the rules of the CAD system, and changing the rules can require a high level of technical knowledge and programming skills.
The nature of city design and planning
All design exercises require a balance between creativity and analysis, between an intuitive approach and a systematic approach. City design and planning usually requires a much more systematic approach than other forms of design because of the quantity and complexity of the information involved.
It is often more of a political exercise and less of a technical challenge, as urban masterplans have to accommodate the complex, sometimes intangible, diverse and changing needs of a large number of people.
Also, because an urban masterplan can affect the quality of life of thousands of people, there is a clear obligation to choose a design approach with a proven track record and high probability of success.
So how can parametric design help city designers?
Parametric design has to be a systematic process because it is carried out by computer software - and in many ways it is ideally suited to city design.
Parametric design involves the automatic generation of design geometry, and a key question is what scale does this automatic generation take place?
At a relatively small scale, like the scale of a street or road, a designer can set parameters such as the width of the pavements or vehicle lanes, specify a path or alignment for the street, and the software can then help calculate the total area of paving stone needed, or the quantity of concrete needed, or the volumes of cut and fill to build the road through an existing terrain.
At the scale of a block, you could set parameters such as the number of storeys, the average unit size, and the depth of a perimeter block, and the software can then generate a visualization and calculate the total floor area of the block and the number of units within it. More advanced generative programs could optimize the height of a perimeter block so as to provide a specified number of hours of daylight to rooms on the ground floor of the block. (The number of hours of daylight would be the key parameter).
Parametric design can also be applied at a much larger scale – algorithms can be written and parameters set that will generate a large masterplan layout. For example, an algorithm could generate a street layout that varies the block size and density based on the distance to transport nodes.
What are the risks of using parametric techniques in city design?
The idea that we can generate an ideal city from a set of principles and logical steps has of course tempted city designers since long before computers were invented. However, generative parametric techniques make it easier than ever before to apply this approach.
It is easy to think that a generated/parametric design is legitimate just because it is based on an systematic process, especially if it happens to look beautiful on screen. However, as with all other software, the output is only as good as the program that creates it. Parametric techniques normally only deal with a narrow part of the city design brief and for this reason parametric technique should not, in themselves, confer legitimacy on a design.
Also, parametric techniques can leave little room for any kind of intuitive, emotional response to a site and its residents, and makes it easy to overlook or exclude vital characteristics that could make a design successful.
Having said this, there’s no reason why large scale generative parametric design shouldn’t be used to explore concepts, as long as it only informs the design process and does not drive it. Parametric software can be so powerful and produce such seductive images that it can require an effort of will (and common sense) from the designer in order to stay in control of it.
The difference between 'parametricism' and 'parametric city design'
The new proposed style of ‘parametricism’ is mainly an aesthetic agenda – assigning value to interarticulation and continuous surfaces while avoiding clear-cut zones/territories, repetition, straight lines, right angles and platonic or hermetic objects.
It’s true that 'parametricism' cannot exist without parametric software, but parametric software can, and does, exist without ‘parametricism’.
Parameters can be applied to rectangular city blocks and there is nothing inherently un-parametric about platonic solids or right angles. Clear-cut zones and territories sometimes work very well in urban planning, and can be dynamically generated by parameters as well. As Patrik Schumacher himself writes, designers "are employing parametric tools in ways which result in the maintenance of a modernist aesthetics, ie. using parametric modelling to inconspicuously absorb complexity."
Our approach to parametric city design software
In our city design software, geometry is only generated at a relatively small scale in the urban context – at the level of streets and blocks as opposed to whole urban areas.
In this way, the designer still relies on their experience and judgement to ‘draw’ the layout of streets and specify the size and shape of each building.
Once it is drawn, the parametric capabilities of the software can then analyse the model and automatically calculate floor areas, residential densities, car parking, energy and resource use, costs, values and other sustainability and quality of life indicators.
If a design is changed – if new storeys are added, or if a street is made wider, or if a land use is changed – then all of the floor areas and other data can be updated automatically, saving a huge amount of time.
When it comes to city design, the real value of parametric technology is not so much in generating geometry at a large scale, but in offering instantaneous feedback of masterplan design information and analysis during the design process.
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