Pavements of Pleasure:

Walking choreographies, visual illusions and emotional landscapes of waiting

Ana Luz,

The Bartlett School of Architecture,

University College London, UK

AbstractPavements are the most banal and ubiquitous form of the urban fabric.

Literally outside the typologies of street furniture and soft landscape design, pavements (sidewalksor footpaths) are crudely defined as the artificially covered and raised walk surfaces for pedestriansat the side of the road. However, as the foremost physical platform of support for locomotion, andthus a connecting element of mapping between body and landscape, pavements could be consideredas experiential constructions of urban exploration. For the urban nomad, here suggested as co-producer with the place-maker, pavements can be the canvas for the city everyday rituals and

narratives, the stage for emotional topographies.Using the site-specific traditional mosaic systems of the Portuguese sidewalks as reference, thispaper will discuss the possibility of a walking notation for urban pavements. Three diverse butlinked conceptual frameworks will be considered: 1. conceptions of aesthetics of mobility and ofdisappearance; 2. principles of optical art, anamorphosis and visual illusions; and 3. theories ofplayability and pleasure.

It will be argued that pavements can deepen the poetics of any given place, in particular theuninspiring spaces of mobility and travel like transport nodes, where spatial practices such aswalking and waiting are embodied by the tempo of empty and negative times of boredom.

KeywordsPavements; Portuguese sidewalks; walking choreographies; visual illusions; playability.

IntroductionWithin environmental design disciplines, hard landscape design usually refers to the built work ofpaving design, landscape enclosures and landscape/street furniture (Lisney and Fieldhouse, 1990).Fundamental to hard landscape design is the principle of construction (techniques and materials),

and also the functional detailing of spaces between buildings where pedestrian movement occurs.This means that the formal and technical qualities of urban settings are utterly related to humanscale, activities and movement. This is certainly the case of paving design and ground surfaceforms, which are typically associated with transport or road infrastructures and pathways’maintenance (repairs, resurfacing and cleaning) but are in fact one of the most important landscapeexpressions.

Spatially speaking, pavements refer to all the durable surfaces of an area intended to sustain eithervehicular or pedestrian traffic. These paving forms are generally connected with the lateral areas ofground on either side of a roadway. More common in modern urban areas, pavements are alsodefined as sidewalks or pathways, which are (foot)paths designed for or by pedestrians (i.e.unexpected trails). Artificially covered with concrete, tarmac, asphalt, brick, stone or even wood,

pavements are constructed as raised walk surfaces that run alongside a thoroughfare (street, way,road). Perhaps due to their prosaic flat quality, they are usually not considered as part of urbanfurniture typologies (e.g. sitting, lighting, information, planting, enclosing and sanitary fittings).

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However, as the foremost physical platform for locomotion, pavements are an integral part of everyurban fabric and one of the key elements of support of people’s basic modes of travel andmovement – i.e. walking and way-finding. Following Tim Ingold’s (2004) proposition of a “cultureon the ground”, this paper discusses a more grounded approach to human movement, landscape

design, and embodied skills of pedestrian engagement and way-finding perception. Often taken forgranted, pavements are more than just the standard finishing of interior floorscapes or outdoorpatchy groundscapes. Programmatically, the physical ground of urban landscapes is normallyentrusted only with service functions (circulation, access, sometimes parking or storage, etc.). Allthe same, in a rather poetic way, the ground pavement can be considered as the stage of everydaylife practices and a valuable built-environment instrument in which to design more emotional

topographies (engaging sceneries, playful settings, and expressive features).

In this sense, it is argued that the science and art of paving forms reveals two importantconceptions regarding the human-environment relationship: firstly, pavements are the connectingpoints or interstitial layers between body and landscape; and secondly, they function and areexperienced as mapping constructions in people’s urban explorations. These two conceptions

suggest that pavements might then deepen the poetics of any given place or particular urbanexperience. This can be the case of the frequently disjointed, monotonous and grey spaces of travelsuch as stations, terminals and gateways; and especially, if to inhabit these landscapes of mobilityimplies frustrating way-finding experiences and the empty and negative times of boredom andwaiting.

By considering exploratory work done outside the liminal scenario of a suburban train station, thispaper proposes the use of pavements as canvas for urban design. For this purpose, the work drawson two important spatial systems: the site-specific traditional mosaic systems of the Portuguesesidewalks as illustrative reference; and, the typographical schemes of notation systems (e.g. dance,movement and music notations) as basis for a walking or way-finding notation at spaces of travel.

Portuguese sidewalksThe Portuguese sidewalks – Calçada Portuguesa – are marked by a simplified and suggestivetechnique of black and white visual game of stone paving tessellation (black and white small cubeforms of calcareous, basalt and granite). This traditional paving art is used in most pedestrian areasin Portugal, and it is usually found in almost every city sidewalks and urban plazas.

The art of paving is believed to have originated in Mesopotamia, where rocky materials were usedto cover the interior and exterior surfaces of constructions. Later adopted by Ancient Greek andRoman civilizations, paving crafts were largely developed by the latter that used to pave all theirempire’s vias using the rocky materials of their surroundings. Introducing particular techniques offoundation and surfacing still employed today in the Portuguese calçada, the Romans also appliedthe paving methods to their building interiors. Here art forms such as the tessella (tessera) or

mosaic configurations were extensively used as remarkable decoration elements and also as anexpressive illustration of everyday reality and ways of living (Matos, 2004). Later, the Arabicinheritance brought some substantial changes to the organizational and structural shape of thepublic pavements, when techniques of draining and empting were developed to the complex cropsystems of dams and waterways. Consequently, the drawing of both the decoration (the arabesc)and the construction preservation of pavements assumed a more public character, spreading the

interior decoration to the streets and giving more visibility to the paving craft as representation ofpolitical, religious and art activities.

In Portugal, the traditional art of paving was further developed after the Renaissance; especiallyafter a series of significant earthquakes in the 16th and 18th centuries (e.g. Lisbon, 1751). As a

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result, cities’ reconstruction would greatly advance urban planning and the modernization oftraditional medieval streets (Matos, 2004). In terms of urbanistic development and accessibility,sidewalks began to be planned together with the adjacent architecture. Several important buildingsand urban squares in Lisbon (e.g. Rossio and Figueira Squares, Restauradores and Liberdade

Avenues) were amongst the first urban spaces and public walkways to be fully covered with largetapestries of stone of black and white drawings. Following roman techniques of mosaic (i.e.bedding and setting of stones), the artistic paving activity was performed throughout the wholecountry and overseas’ colonies (e.g. Brazil) by hundreds of calceteiros craftsmen (pavers), whowere in charge of the construction of new streets’ pavements, novel techniques for tessellations, tilepatterns and aesthetic compositions. Particular motifs such as the “wide sea”, the “interwoven

ropes”, the Portuguese Discoveries’ caravels and numerous representations of daily practices,became symbols of Portuguese culture and part of a pictorial language impressed upon the ground(Bairrada, 1985). Traditional pavements soon became a mean of communication which told thehistory of the place and the everyday narratives of its users, also promoting the pedestrian pleasureof ‘going for a walk’ (passeio público). Artists and writers alike who lived and walked throughthese stoned engravings literally praised the poetry of pavements’ chromatic games, the skill

process of laying stones and the embodied feelings of such painted topographies (Cabrera et al.,1990; Matos, 2004).

Figure 1 – Portuguese sidewalks: pavers, pavements and patterns

Unfortunately, the art of paving slowly became restricted to conservation works in historical areasor important top architectural projects. This was due to factors such as: the high cost and reduced

robustness of traditional paving (in comparison to concrete-based or bituminous materials); thecraftsmen’s arduous labor of laying stone by stone while squatting down; the scarcity of materialresources; the municipalities’ low budget; and also the present ‘barrier-free’ regulations for streetaccessibility. However, despite economical and manufacture limitations pavements have recentlybecome a source of inspiration as aesthetic expression for several artists, who transferred the color,techniques and mosaic composition to both the inside of architecture surfaces (e.g. Chiado) and the

exterior road surfaces of vast new urban interventions (e.g. the urban area of Parque Expo, formerLisbon Park Expo’ 98). Although now subject to fewer applications or technological adaptations,Portuguese pavements continue to be a strong cultural manifestation. The memory, culture andurban landscapes of Portuguese identity will be forever immortalized in the artistic stonedpavements of the sidewalks (Bairrada, 1985; Cabrera et al. 1990; Matos, 2004).

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Walking choreographiesIn their recent work Groundscapes, the architectural team Textbild proposes: “analogous to a planstretched out on a drafting table, the ground is programmed as canvas of a picture that can be

grasped as a whole […] to organize space” (Ruby and Ruby, 2006). Extending the architecturaldrawing into the horizontal surfaces of the ground, the authors suggest the conception of “inscribedground”. The inscription of an image into the ground transforms the lines, points and surfaces of asimple drawing into a topographical relief with several urban structures and programmaticelements, which users in turn tend to “experience haptically, crawling like ants across its surfacewhile attempting to grasp its meaning through touch” (Ruby and Ruby, 2006). This ‘touch’ refers

not just to the sensory ability of hand tactility, but to an embodied experience of pedestrianmovement, thus including the visual, auditory and locomotion body perception.

Challenging the “groundlessness of modern metropolitan dwelling”, Ingold argues for a moregrounded approach to spatial perception, in which pedestrian experiences and walking activitiesshould not be reduced to short intervals between other vehicular movements and to which feet are

considered as mere “stepping-machines” (Ingold 2004). By proposing a balance of the senses as analternative to the typical visual and manual modalities, Ingold suggests restoring the haptic andkinesthetic sensations of touch through the feet (albeit mediated by footwear), which are literallypeople’s foremost continuous points of contact with their surroundings. Hearing with the feet,observing through a continuous itinerary of movement or feeling the ground through the wholebody are just some of the challenges that a new pedestrian touch may reveal. Undoubtedly that the

study of pedestrian behaviors, spatial navigation processes and “walkability factors index” (Stonoret al., 2002) are crucial for forecasting pedestrian flows and modeling pedestrian movement in lightof changes in urban configurations. However, one is more interested in the ‘intangible notation’defined by everyday walking choreographies (i.e. steps arrangements, sequences and directions;movement routines and designs; feet pressure and intensity; way-finding dances and pauses).

A walking choreography happens, for instance, within everyday practices of coming and going in-and-out spaces of travel like train stations. Here, pedestrian operations such as lingering, stoppingor temporarily pausing, occasional standing, fidgeting, stalling ‘time’ and disconcerted walkingoften occur. These practices define, one argues, the contemporary emotional landscapes of waiting.As with fingerprints, pedestrians’ density, cross-currents and feet pressure ‘leave behind a trace’ offeetprints and motion uses that subliminally are impressed on to the groundscape. Hypothetically, if

pavements could then act as ‘living organisms’ and capture, react or change according to theseground imprints, a walking notation or a way-finding system of pedestrian touch could be bodilysketched. A pavement walking notation is like stepping or drawing on sand; or creating endlessephemeral stencils that overlay each other; or even gently pressing electroluminescence conductivematerials that change color or pattern with pressure touch and temperature. Since walking involvesmotion perception, a temporary notated language as such could follow some of the principles of

dance, music and movement notations. Hence, comparable to Portuguese sidewalk typologies, itsgraphical representations would become the motifs of the pavement drawings and ever-changingpatterns.

Aesthetics of disappearance and of mobilityThis time-based body impact of motion perception and the pedestrian process of (de)codification

(walking notation) are to some extent analogous to Paul Virilio’s notion of “aesthetic ofdisappearance” (Virilio, 1991). This refers to both the experience of change under speed (e.g.watching the landscape quickly ‘passing by’ through a train window) and to its insubstantial orfleeting visual representation. This ‘dematerialization’ of the visible was explored, for instance, inkinetic art where the disappearing movement was registered through a series of momentary

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postures and ‘freeze-frames’, introducing contemporary explorations of ‘trace forms’ in dancenotation. Although originating in the arts, the aesthetic of disappearance is an interesting designstrategy for the ground level of landscapes of waiting, where the deliberate organization of a way-finding path and the topography around it may turn motion perception into an aesthetic experience.

Depending on walking and waiting time intervals and durations, objects and terrains can beexperienced as multi-sensory perceptual artifacts, varying in the degree of focus (e.g. details suchas pavement textures fading or changing with pedestrian movement) and meaning.

Similar to this aesthetic of disappearance, Ossi Naukkarinen proposes a ‘moving field’ of aestheticmobility (Naukkarinen, 2005). This refers to the aesthetic and/or artistic aspects of mobility and

change, which relate people’s ways of moving with aesthetic approaches and choices. He states:“our everyday mobility consists of various ways of getting about, and sometimes our approach tothem is aesthetically colored: we pay attention to how beautiful, ugly, fascinating or enthralling awalk, a drive, or a route is”. Naukkarinen suggests that these ‘sensuous’ and structured acts ofmoving about offer intense kinetic, visual and auditory experiences, which imply that mobileactivities can often be considered as aesthetically rich phenomena.

Beyond the primary purpose of moving (i.e. to get somewhere else), the search for aestheticsexperiences and environments is often one of the reasons for travel. However, arguing against thecontemporary mindset obsessed with speed, mobility and efficiency, it is also important to considerthe notions of ‘temporary occupancy’ and ‘momentary stillness’. Ultimately, the final purpose ofwalking or moving is to stop. While traveling, and in particular before and after a journey, there are

usually occasions of interruption, pauses between moments of mobility. Those are normally thefirst moments of encounter with the space traveled from and to. For instance, at train stations whenleaving the train to encounter the city ahead or vice-versa. This means that a mobile aesthetics, anaesthetic of mobility or even of disappearance, are also defined by a waiting discontinuity. Bothbodily motion and stillness help to determine people’s perception and appropriation ofenvironmental features – i.e. the ‘appearance’ of the world (Ingold, 2004). Certainly, there is a

difference between moving about by oneself and observing movement or mobility from astandpoint, either standing still outside or moving inside a vehicular capsule (Naukkarinen, 2005).These mobile variances shift pedestrians’ aesthetic valuations as the experience of sensoryperception unfolds and changes through these diverse choreographies.

What is interesting here is that the pedestrian, mobile or at rest, participates in the construction of

its surroundings through multiple paths of observation, motion and emotion (Ingold, 2004). Whileon foot, with strides and pauses, a walking choreography is the primary act of ‘transformation’ ofthe territory/landscape. As Francesco Careri proposes, walking is an “aesthetic practice”, but alsoan “aesthetic instrument of knowledge” (Careri, 2002). Ingold supports this interrelated notionbetween aesthetic perception, cognition and locomotion, by suggesting that “walking [is] a form ofcircumambulatory knowing” and that people know as they go, not before they go (Ingold, 2004).

These conceptions focus on the embodied process of moving per se and its transitory andtransformational states, rather than on the contemporary modality of vehicular mobility. In thiscontext, one argues that the experience of pedestrian touch is not just marked by the modernnomadic lifestyle of accelerated mobility, constantly being ‘on-the-move’ or ‘in transit’; but, isinstead defined by the pedestrian ‘slow-motion’ rhythms of everyday life, by the ‘stop-motionanimations’ that happen in between.

Animating anamorphic topographies and visual illusionsFollowing Ingold’s proposition that perception is a function of movement, it is possible to infer thatwhat people perceive in their surroundings depends on how they move through them. This simpleconjecture can provide paving design some directions and allusions. A walking choreography

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through a landscape [of waiting or not] is informed by a sequence of distances and projections (e.g.images in perspective, sounds in distance), which people construct as they go based on theirsensory perception or pedestrian touch. Contrarily to graphical perspective, this motion throughpaths and ‘lines of sight’ implies multi-focal and multi-direction connections. In theory, this

‘cubist’ construction of circumambulatory knowing would (arguably) provoke ‘momentarydistortions’ similar to that of a kaleidoscope or mirrors’ room; but, in reality these multi-focaljuxtapositions rarely occur. Nevertheless, one could ask: what if a distortion of a sensoryperception could be captured within the surroundings; what if pavement landscapes could besqueezed and stretched in sensory illusions as if through anamorphic lenses?

There are several types of sensory perception distortions (e.g. optical, auditory, touch illusions),which are ‘misinterpretations’ of a true sensation perceived in a distorted manner. Each of thehuman senses can be ‘deceived’ by illusions, but visual phenomena and optical trickery are themost well know. Optical or visual illusions exploit errors of perception (phenomena of illusions) orassumptions made by the human visual system (usually their basis is in the visual pathway and notin the optics of the eye), into incorrectly perceiving what is present or perceiving something that is

not present at all (Coren and Girgus, 1978). There are physiological illusions that occur naturally(e.g. afterimages and perceptual aftereffects), and cognitive illusions that are caused by amisapplication of perceptual knowledge to interpret or read sensory signals (Gregory, 1997).Cognitive illusions are commonly divided into: ambiguities, or ambiguous illusions, which arepictures or objects that elicit a perceptual change between the alternative interpretations (e.g. thefigure-ground Rubin vase); distortions, or distorting illusions, which are characterized by

distortions of size, length or curvature (e.g. the Mueller-Lyer ingoing and outgoing arrow-headsillusion); paradoxes, or paradox illusions, that are generated by paradoxical or impossible objects(e.g. the Penrose triangle); and fictions, or fictional illusions that are defined as the imaginaryperception of objects by a single observer such as delusions and hallucinations (Coren and Girgus,1978; Gregory, 1997; Wade, 1990).

Inspired by the optical characteristics of the eye and the laws of visual perception, optical illusionswere adopted, explored and manipulated by the 1960s artistic movement Op Art. Through hard-edge and abstract compositions Optical artists explored the arrangement of serial structures andgeometrical forms or patterns to create striking visual effects of movement and vibration, withimpressions of flashing, swelling or warping and hidden images (Wade, 1982). By sharingacademic theory about the relationships between body, time, space and movement, Optical art was

developed in parallel with Kinetic art in the 1960s and 70s, which underlying principles of chanceand randomness are based on real or illusory, mechanical or random sequences of movements.

Also exploring mathematical and physical rules of perspective and visual perception, there areanamorphoses or anamorphisms. These are unconventional perspectives or unintelligibledistortions of elongated or swirled smears of shapes and lines that only reassemble themselves as a

coherent image when viewed from a particular extreme angle, or in a convex or trapezoid mirror(Baltrusaitis, 1977; Warner, 2004). Since the Renaissance, the geometrical technique ofunconventional perspective through anamorphosis has been largely explored in painting andprintmaking, which designs are based on visual compositions of deformed, doubled orhidden/secret images (Leeman et al, 1976). A particularly well-known example is the obliqueanamorphosis of a skeleton distorted image in the painting The Ambassadors by Hans Holbein,

1533. In anamorphic art, the images do not make sense unless the viewer knows how or where toplace the ‘eye’ or move either the image or himself around it. To some extent, that is the case of the‘anamorphic’ designs of road markings. In order to be viewed by road users from moving andshallow angle positions, some road markings vary the vertical dimension of the lettering (e.g.stretching technique), exploring the apparent shrinking effect (foreshortening effect) of visualperception when the observer is moving at speed.

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A common element present in all these perceptual illusions and visual allusions is the ‘distortion ofreality’ or ‘changing perspective’, either graphically represented or physically embodied by theobserver’s movement. By exploring this element of embodied movement, it is argued that thedesign of paving landscapes can ‘play’ with sensory perception illusions as to create physical

anamorphic topographies. The following images show some proposals for paving design and mock-up explorations of flat and 3D anamorphic constructions, which use ‘weaving’ techniques andoptical, auditory and touch illusions as design techniques for the pavements way-findingplayability.

Figure 2 – Design explorations: weaving pavements and anamorphic topographies

Playability and pleasureThis paper argues that playability can be explored as design criteria, fostering imagination,immersion and enjoyment. As a theoretical concept, playability is difficult to define since itcomprises a wide range of practices of learning, leisure and free-time. Usually, it refers to ‘non-serious’ activities of recreation and enjoyment, or any other entertainment activities that act as

work antithesis. More frequently, playability is associated to the degree and quality of an activitythat is structured and goal-oriented such as ‘to play a game’. However, in lay terms, the concepts ofplay and playability are intrinsically related to experiences of ‘having fun’ and thriving onsatisfaction achievements – also known as gratifying playful pleasures.

The notion of pleasure was greatly explored by the anthropologist Lionel Tiger (1992), who

defined not a universal explanation for the concept but rather a framework of four interrelated typesof pleasure. Firstly, there are the physio-pleasures, which are related to the body and the senses,deriving from the sensory receptors and including feelings of sensual and sexual pleasure.Secondly, there are the socio-pleasures, which are associated with inter-personal and socialrelationships, deriving from the enjoyment of being in the company of others – social interactionsand social identity. Thirdly, the psycho-pleasures are linked to the mind and derive from the

satisfaction and fulfillment of accomplishing a task. And finally, the ideo-pleasures which arerelated to emotions and values, deriving from the appreciation of ‘abstract’ entities (e.g. art ormusic), and also associated with the aesthetic principles of objects and settings’ environmentalperception (e.g. balance, harmony, complexity, and other Gestalt principles of organization).

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The difficulty of generally defining what is and what constitutes ‘pleasure’ is due to the fact thatpleasures are so idiosyncratic, private and immeasurable; but, it is also this indeterminacy whatmakes it so powerful and playfully intriguing (Tiger, 1992). To some extent, one could argue that itis precisely this individual attitude towards the pursuit of satisfaction and the power of pleasure

that informs the level of pleasurability and playability people draw out of any given interaction.Through captivating experiences of involvement, challenge, immersion, investment, internalchange and social interaction, people persistently explore the power of play and pleasure and theambiguity of playability.

In order to explore a ‘theory of playability’, a brief outline of the theory of play should be briefly

presented. Johan Huizinga’s (1938; 1998) seminal book “Homo Ludens” advanced play not as aninconsequential and biological phenomenon confined to the sphere of childhood, but rather as acultural one – i.e. a special form of activity separated from everyday life with a social functionwhich involves experiences of great fun, pleasure and enjoyment. Another classic in play theory isRoger Caillois’ (1961) work “Man, Play and Games”, which extended and in part disputedHuizinga’s claims, by suggesting that the power of play is important to culture insofar as playthings

as games, toys and other entertainment gadgets are historical residues of culture and the foremosttriggers for playful activities. Caillois’ typology of play (competition –agon, chance –alea,simulation –mimicry, and vertigo –ilinx) also yielded another valuable concept: the notion of acontinuum between free play or improvisation (paidia) and goal-oriented and rule-bound play(ludus). This contribution about ‘freedom and rules’ is regarded as the first conceptualization ofplay and game as complex systemic interactions, instead of straightforward leisure activities or

cultural practices. In terms of game theory (following from the mathematical theory of games thestudy of strategies in a variety of situations), Brian Sutton-Smith’s (1997) book “The Ambiguity ofPlay” contributed further to this view of structured games by developing notions of control andsystem and thus proposing play as an exercise of voluntary controlled systems. The application ofpure play theory to game studies and its relationship with rules and computer game design is alsoextensively discussed by Katie Salen and Eric Zimmerman (2003) book “Rules of Play: Game

Design Fundamentals”, which reveals a contemporary tendency to associate the concept of playwith the word game-play, in particular in media studies, game theory and Human ComputerInteraction research. Ultimately, the concept of play can also be positioned within the post-modernliterary and philosophical domains of Deconstructivism, which uses play as a programmatic termfor the process of signification (semiotics) and the reconstruction of language and narrativebetween the realms of the imaginary/fictive and real life. Similar to game storylines, the literary

text is the result of a process of fiction-making, to which play is the mode of mediation betweenreality and imaginary worlds.

Conclusions: playing with paving designFollowing the previous outline of play and game (i.e. activities of fun and playful satisfaction), it ispossible to draw a parallel between the previous conceptions of ambiguities, distorting realities,

paradoxical illusions, fictional worlds and embodied movements with the concept of playabilitypleasures. Since the ‘playfulness’ and pleasure taken out of any given interaction is directly relatedto the user participation, involvement, immersion, investment and satisfaction, it should be thisplayful diversity of users’ experiences, capabilities and expectations that should inform the designof our surroundings. This means, for instance, that the design of pavement landscapes shouldinvolve the user as co-producer in ‘designing’ or defining a playful space.By suggesting pavements

of pleasure, anamorphic landscapes of illusions and way-finding walking notations, the experienceof space and time (e.g. when waiting or traveling) may be challenged, accentuated or enhanced. Inspaces of travel and landscapes of waiting, pavements as such may provoke playful experiencesand choreographies, suggesting new conceptualizations for aesthetic mobilities. Nevertheless, tofurther assess these prepositions, more experimental design work in this area is needed.

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Baltrusaitis, J. (1977) Anamorphic Art. Cambridge: ProQuest Information and Learning Ltd.

Cabrera, A., Nunes, M. and Ruas, H. (1990) Olhar o Chão: a Glance at Portuguese MosaicPavement. Lisbon: Impressa Nacional-Casa da Moeda.

Careri, F. (2002) Walkscapes: Walking as an Aesthetic Practice. Barcelona: Gustavo Gili.

Coren, S. and Girgus, J.S. (1978) Seeing is Deceiving: the Psychology of Visual Illusions.Hillsdale, New Jersey: LEA Publishers/ John Willey & Sons.

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Stonor, T., Arruda Campos, M.B. and Smith, A. (2002) “Towards a walkability index”. Walk 21C– 3rd International Conference Steps Towards Liveable Cities, San Sebastian, Spain.

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Wade, N. (1982) The Art and Science of Visual Illusions. London: Routledge & Kegan Paul.

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Warner, M. (2004) “Camera Ludica”, in L. Mannoni, W. Nekes and M. Warner (eds.) Eyes, Liesand Illusions, pp. 13-23. London: Hayward Gallery/ Lund Humphries.

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