1 Introduction

The survey and associated mapping of odors in space is now an increasingly growing field of research in the (social) spatial sciences. A meta-analysis by Xiao et al. makes this particularly clear: in the last ten years (as of 2021), the study of olfactory landscapes has increased exponentially. This has been accompanied by a corresponding increase in the need for mapping methods in this field (Xiao et al. 2021, pp. 1–2). It is not possible to simply fall back on tried and tested cartographic methods for this relatively new research subject of odors or olfactory landscapes. For the survey, measurement and mapping of physical objects in spaces, we can look back on a millennia-old history of development: from the, often seemingly fantastic, maps of antiquity (cf. Keith 2013), such as Ptolemy's map, which was surprisingly accurate for its time (for a reconstruction of this see: The British Library 2022), to the partly schematic (but practical) representations of the European Middle Ages, such as the tabula Peutingeriana (Talbert 2007) to today's countless projection methods, which are sometimes more, sometimes less appropriate depending on the area of application, we are looking at constant development of the methods of representing our environment. This journal, in which this article now appears, is an equally good example of this.

The mapping of odors, by comparison, is still in its infancy. For a long time, the experience of odors, their occurrence, and their origins were recorded exclusively in text form (see in detail Classen et al. 1994). We can probably date the first real, partly systematic mapping of olfactory experiences to the eighteenth century. Jean-Noel Hallé's walks along the Seine in Paris, during which he mapped the emerging odors, can possibly already be interpreted as the first smellwalks with subsequent mapping of a smellscape, even if these served rather to locate possible sources of illness (cf. Margolies 2006).

However, a real systematic recording and representation of olfactory phenomena in space began much later. For a long time, the cartographic representation of the perceptible environment continued to be limited to that which could be captured visually. This changed only with an increasing interest in the study of acoustic phenomena and their mapping, which from the 1960s increasingly focused on the acoustic environment, i.e., acoustic space, and thus also developed new methods of representation. Of particular interest here might be the extension of the purely visually perceptible map by the acoustic dimension, which also includes the actual reproduction of the 'recorded' acoustic phenomena (the so-called multimedia cartography) (Dodt et al. 2017, pp. 263–264). One reason for the increased emergence of audiovisual maps or maps that treat (and partly reproduce) acoustic phenomena may also be the expanded technical possibilities of the last decades of the previous century (see in detail: Siepmann 2021). An 'expansion of the senses' then took place again in the 1980s and 1990s, where now, in the light of the previously 'discovered' auditory or audiovisual cartography, a cartography of olfactory space began to take root (Dodt et al. 2017, p. 264). The most important pioneer of this new research direction is probably J. D. Porteous, who in 1985 for the first time introduced the concept of olfactory landscapes, i.e., smellscapes, into the discourse of human geography (Porteous 1985). Today, there is a growing interest in olfactory issues in the (spatial) sciences and their cartographic implementation (cf. Xiao et al. 2021).

The fact that the research and mapping of olfactory phenomena have only recently received greater attention has several reasons. First of all, it should be clear that visual and acoustic sensory stimuli are easier to record and write down than those associated with more 'abstract' senses, such as smell, taste and touch (Eisewicht et al. 2021, p. 7). Even today, positivist research approaches in the olfactory field such as odor monitoring and other attempts at quantitative measurement of the distribution and occurrence of odors quickly reach their limits (Lammes et al. 2018, pp. 64–65; Perkins and McLean 2020, p. 156). For example, survey methods that aim to measure the number of different molecules that can be perceived as an odor fail because of the sheer complexity of many odors, which are often a mixture of hundreds of different chemical compounds (Bushdid et al. 2014, p. 1370; Margolies 2006, p. 110). The scent of one rose is not exactly the same as that of another. On the other hand, the centuries-long devaluation of the sense of smell in the sciences makes it difficult to deal with this topic in detail. This neglect, especially in the social sciences, has also led to the fact that so far there have only been isolated attempts to locate olfactory topics theoretically (see e.g., Raab 1998). Often, for example, we still find ourselves in descriptive olfactory landscape research, in which the theoretical background is often only implicitly touched upon without actually formulating it in greater depth. This will be done here by viewing olfactory landscapes as social constructs which, in addition to the socially constructed component, also have strong phenomenological features (which take into account the very individual character of olfactory perception). This theoretical positioning makes it possible not only to describe the presence of odors (and the resulting olfactory landscapes) but also to investigate their emergence and meaning in more detail. This makes it possible to broaden the horizon of this field of research immensely (the following chapters will deal with the neglect of the sense of smell in science and philosophy as well as a further explanation of its theoretical positioning).

New approaches to the field of odor research must therefore be chosen to avoid the pitfalls and problems described. This requires an examination of the epistemological approach to the field and thus of the understanding of the research object itself, as well as the (further) development of new survey and presentation methods. This article aims to make a contribution to this by addressing the now-established concepts of smellscape mapping and, along with it, their collection and representation. Furthermore, the theoretical approach to the field will be elaborated to anchor smellscapes on a phenomenological-social constructivist foundation. This article is based on a master's thesis on the construction of olfactory landscapes in which different ways to construct Christmas landscapes were identified (see Endreß 2022). This paper on the other hand takes some of the found results and discusses them in relation to surveying and mapping these landscapes.

2 The Theoretical Framework: Social Constructivism and Phenomenology

As has already become clear, the experience of smells may be described as a highly subjective experience. We often (involuntarily) become aware of this in everyday life, regardless of whether the perfume advertised in the highest terms suddenly makes our partner gag or whether the often highly praised fresh country air smells to us only rather unpleasantly like a cowshed. For such an object of research, two approaches, in particular, come into focus in the olfactory research undertaken here: phenomenology and social constructivism. Through a neopragmatic approach, these two approaches (both of which can be traced back to Alfred Schütz) can be intersected, whereby these approaches complement each other. A neopragmatic approach helps to deal with complex questions (such as the meaning and interpretation of smells and spaces), as it enables the use of different theories, methods and perspectives in an object-oriented (resp. goal and result-oriented) way to open up the most appropriate access to the research field (Kühne and Berr 2021, p. 201; for a brief introduction to neopragmatic approaches in human geography and landscape theory see Kühne and Koegst 2023, pp. 8–12).

Phenomenology is essential to emphasize and focus on the subjective, direct experience of a phenomenon (in this case smell) (Kühne 2019, p. 136). The sensory perceptions thus form the basis of all knowledge (Eberle 2021, p. 34), because only these make it possible to experience a phenomenon at all. This recourse to the subjective experience of a sensory impression seems to be particularly promising in the case of odors for various reasons. Not only do odors establish a relationship between the perceiver and his spatial and social environment (Bischoff 2007, p. 43), but these sensory impressions also seem to trigger stronger and more emotional reactions in us humans than would be the case with other stimuli (Bischoff 2007, pp. 44–46; Porteous 2019, p. 22). One possible explanation for this could be the structure and evolutionary development of our brain: olfactory stimuli enter the amygdala and the hippocampus very directly, the areas of our brain in which emotions and memories are processed, without first flowing through the thalamus, which initially takes on a mediating and (further) processing function for all other stimulus information. Smell information, therefore, arrives 'unfiltered' in the amygdala-hippocampus complex (Hatt and Dee 2009, pp. 55–58; Herz 2011, p. 271; Puelma Touzel 2013). This could be one of the reasons why it is sometimes assumed that olfactory impressions evoke particularly strong and direct reactions. Furthermore, it seems reasonable to assume that the brain areas that process memories and emotions are particularly closely related to the perception of smell from a neuroevolutionary point of view since they developed from neural tissue that can be assigned to the (formerly) olfactory cortex (Herz 2011, p. 272). It thus becomes clear why recourse to phenomenology can be very fruitful to examine subjective olfactory experiences. At the same time, due to this inherent subjectivity, it must not be assumed that the insights obtained in the process are not transferable, i.e., that they remain in purely isolated subjective experience. Schütz refers to the everyday lifeworld in which the individual finds himself. This everyday lifeworld is unquestionably and naturally real for the individual (Schütz and Luckmann 2017, 30). Since this world is intersubjectively comprehensible, it must logically be assumed that other individuals experience this everyday lifeworld at least similarly, i.e., also perceive its inherent objects or phenomena similarly and thus construct this world similarly (Schütz and Luckmann 2017, pp. 30–31).

'Construct' is now the appropriate keyword to go into the second theoretical basis, social constructivism. Basically, social constructivism focuses on the construction of perceived reality on the basis of patterns of interpretation and discourse that have been learned and continuously developed in a social context. The (partially) socially accepted patterns of interpretation and discourse are imparted from childhood onwards. This socialization initially takes place primarily through "significant others" (Berger and Luckmann, 1966/1991, p. 151) and is subsequently reproduced (Berger and Luckmann 1966/1991, pp. 150–151). Since we are explicitly talking about olfactory landscapes here, it seems useful to discuss the social constructivist theory of landscape in more detail. According to this theory, there are no 'true' or 'absolute' landscape concepts in the essentialist sense. Rather, the understanding of landscape is also subjective and subject to social norms. Thus Cosgrove concludes logically when he emphasizes: “Landscape is not merely the world we see, it is a construction, a composition of that world” (Cosgrove 1998, p. 13). Landscape is thus only created through the 'glasses' of the observer. The viewer, and here we should refer to Löw (2015)’s understanding of space, synthesizes the objects of space to form the space 'landscape' (Löw 2015, pp. 159–160). The background of the observer, i.e., his cultural-social socialization, as well as his individual experiences, determine how the objects are placed in relation to each other, or how the associated filtering is carried out (Greider and Garkovich 1994, p. 1). From a social constructivist perspective, landscape must therefore be located at the intersection of physical objects, person, and society (Kühne 2018, p. 55) whereby the patterns of construction, i.e., the criteria according to which a space is then perceived as a landscape, are constantly evolving, as they are subject to social negotiation processes (Kühne 2018, p. 57).

In this theoretical basis, olfactory landscapes can also be approached further, as they seem to be highly subjective on the one hand, but on the other hand, also seem to be subject to societal and cultural patterns of interpretation (this will be discussed in more detail in the following chapters; for a deeper discussion of (changing) societal-cultural patterns of interpretation of odors, please refer to Classen 1993; Classen et al. 1994; Endreß 2022; Raab 1998). Olfactory landscapes should therefore be understood as follows: Olfactory landscapes represent social constructs which are constructed by the subject in the synopsis of odors, against the background of (partly) social patterns of interpretation and discourse as well as personal experiences (Endreß 2022, p. 19).

3 The Visuality Paradigm: Eyes First

In the sciences, we have to look back at the neglect of olfactory stimuli, their significance, and their added value for our understanding of reality that has lasted for centuries by now. This problem does not stem solely from the abstract existence of odors and their complicated survey. Rather, for a more comprehensive understanding of the perception of olfactory themes in the sciences, one must also take a closer look at the underlying philosophical discourse (for a detailed account of this see Classen 1993; Endreß 2022; Raab 1998). Bischoff speaks here of the visuality paradigm anchored in Western societies (Bischoff 2007, p. 33). This refers to the overvaluation of the sense of sight with the simultaneous disqualification of the sense of smell, or the other senses (Bischoff 2007, p. 33; Eberle 2021, p. 33). In geography, especially in relation to landscape research, this paradigm is evident, for example, in Cosgrove's work on the social construction of landscapes, in which “the argument of the eye” (1998, p. 31) is also at the center of gaining knowledge in the very end (see also Bischoff 2007, p. 18; Cosgrove 1998, pp. 27–31). This visuality paradigm led to an enormous loss of social as well as scientific relevance in the ‘Western world’, which is why Classen also concludes that “no sense has suffered such a reversal of cultural fortune as smell” (Classen 1993, p. 15).

The subordination of the sense of smell to other senses can be traced back at least to Aristotle. He already classified the senses according to the importance attributed to them. He placed the sense of smell behind the sense of sight (which is in first place) and the sense of hearing (in second place) (Hasse 2005, p. 38; Raab 1998, p. 36). In the centuries that followed, the importance of scents in society as a whole declined continuously in the ‘Western world’. Of course, fragrances did not disappear from people's everyday experiences; even after Aristotle’s evaluation, they continued to play an important role in the lives and beliefs of the Western population (Classen 1993, p. 17; Endreß 2023; Hatt and Dee 2009, pp. 27–30; Raab 1998, pp. 64–84). Nevertheless, a clear decrease in the attributed relevance can be seen in the overall view, especially, for example, through the Enlightenment, which clearly located the sense of sight as the “revealer of the truth” (Classen 1993, p. 28). The Reformation also had a great influence on the perception of smells. While in Catholicism scents, above all incense, which Hatt and Dee call the ‘barn smell’ of the Catholics (2009, p. 28), are of great importance, in Protestantism these mystical rites should be refrained from (Classen 1993, p. 28). A general rejection or devaluation of the sense of smell is also noticeable when looking at (among others in the German region) influential philosophers, with Nitzsche as a significant exception (Raab 1998, pp. 45–47). The loss of importance of smells or the sense of smell continued into the twentieth century, where now “visualism could reign unchallenged in both art and science, and in the home” (Classen 1993, p. 35). However, Classen goes on to postulate a renewed increase in the significance of the sense of smell and smells in general in postmodernity (Classen 1993, pp. 35–36). The emerging discussion in the (social) sciences about a sensorial turn towards a stronger preoccupation with non-visual sensory impressions (vgl. Eisewicht et al. 2021), as well as the increased research interest in olfactory topics already described at the beginning, (vgl. Xiao et al. 2021) also supports the assumption that the prevailing visuality paradigm is being partially broken.

In contrast to the very long-lasting loss of importance of smell in the ‘Western world’, there are also cultural circles in which smell is clearly more important. A very impressive example of this is the native people of the Andaman Islands, who are probably one of the most odor-centered groups of people in the world. They arrange their entire worldview, religion, space, and time conception on the basis of smells, its coming and going (Classen 1993, pp. 126–131; Lammes et al. 2018, p. 62; see in detail: Pandya 1993; Raab 1998, p. 49). This illustrates, even if only exemplarily, that a different conception or value system with regard to odors is quite possible and exists.

4 Smellscapes Today and Further Development of Existing Concepts

Research into smellscapes and the mapping of them, which is in its infancy, is slowly beginning to run its course, to experiment. New approaches have been tried and developed since the research of olfactory stimuli entered the geographic discourse in the 1980s and 1990s (Dodt et al. 2017, p. 264) and Porteous first introduced the concept of smellscapes (although it should be mentioned that French cultural geographers discussed the geography of odors already in the late 1940s (Dodt et al. 2017, p. 264)). Foremost among these are the work of Henshaw (2014) and McLean (McLean 2016, 2017, 2019, 2020; Perkins and McLean 2020) for example, who have pioneered and continue to pioneer in this regard (cf. Eberle 2021, p. 42). At the same time, however, it is also clear that this field of research is still at the beginning of its journey. So far, there are no uniform guidelines for the collection and creation of smellscapes. The topic is currently much more in an experimental phase, in which different approaches are redesigned, blended, further developed, and also discarded again (Lammes et al. 2018, p. 88; Perkins and McLean 2020, p. 159; for a detailed overview of existing methods of olfactory mapping and data collection see: Dodt et al. 2017).

If we look at the different methods used to survey olfactory conditions, including landscapes, we can first distinguish between indirect and direct survey methods (Dodt et al. 2017, p. 265). The indirect survey methods mainly comprise literary works that include the olfactory dimension. Here, all literary genres come into consideration, i.e., from travel guides and memoirs to novels and fiction, and recently there has also been an increased focus on contributions from social media (Dodt et al. 2017, p. 266). Thus, experienced olfactory experiences, such as the scent of lavender on a bike ride in Provence can be gleaned from a travel blog (Englin 2019), or fictional olfactory landscapes such as those of eighteenth century 'stinking' Paris in Süskind's ‘Das Parfum’ (Süskind 2006). It is clear, of course, that we are mostly not dealing with systematically surveyed olfactory landscapes here, but rather reflecting personal experiences or personal perceptions and clichés (albeit sometimes linked to research). This might therefore also be one of the reasons why Dodt and colleagues point out that this form of olfactory survey is only of limited use for reconstructing olfactory spaces. At the same time, however, they highlight the usefulness of these sources to reconstruct, especially from older documents, possible olfactory landscapes of past times, which in turn allows contrasting them with today's olfactory landscape to some extent (Dodt et al. 2017, p. 266).

In contrast, the direct survey of odors or olfactory landscapes attempts to systematically record odors, and here, too, a variety of different methods seem possible. As a positivistic approach, different types of quantitative surveys can be mentioned, which aim to capture the concentration as well as the distribution of odors (Lammes et al. 2018, pp. 64–65; Perkins and McLean 2020, p. 156). In this context, technical sensory measurements offer the possibility to measure the concentration of olfactory-relevant molecules (Dodt et al. 2017, p. 268). However, these systems quickly reach their limits due to the complexity of many odors, as odors often represent a composition of hundreds of different molecules (Bushdid et al. 2014, p. 1370; Margolies 2006, p. 110). In addition, there is an interpretation problem with the odors measured in this way, since the (often very individual and subjective) odor perceptions of people (see Endreß 2022, for further details) cannot be appropriately inferred in this way (Dodt et al. 2017, p. 268; Raab 1998, p. 16). One attempt to solve this problem is represented by human-sensory measurement methods, i.e., those that actually use people's noses as measurement instruments. As Dodt and colleagues show with reference to various measurement specifications, these can be highly structured and standardized in order to enable the highest possible objectivity despite the subjective object of study (Dodt et al. 2017, pp. 267–268). In contrast, there are more subjective, less standardized procedures, which will now be briefly discussed, since the study presented here and its results also belong to this category.

First of all, it should be elaborated which epistemological approach was used for the investigation and the further development of the presented smellscape methodology. As already mentioned, a positivist approach to olfactory landscapes can be chosen, but this has some limitations, especially when the olfactory landscape perceived by humans is the focus of the investigation. These limitations will be briefly explained below. On the one hand, there is the aforementioned measurement problem; odors can hardly be quantitatively surveyed in such a way that deeper insights into the olfactory perception by people can be concluded; it remains with a pure analysis of the chemical composition of the odor-producing components. This interpretation problem is based on various factors (for more details see Endreß 2022): Starting with bodily peculiarities (such as a COVID-19 infection (Mizrahi et al. 2020) or a simple cold (Hatt and Dee 2009, p. 48)), the environment as well as the weather in which the odor occurs (Hirsch 2006, p. 187; Lammes et al. 2018, p. 59; Perkins and McLean 2020, p. 167) as well as the social and cultural background of the smelling person (for more details see, among others, Classen 1993; Classen et al. 1994; Endreß 2022; Raab 1998), all these factors determine how people perceive and interpret an odor impression. However, quantitative measurement methods of molecular composition cannot include all these factors. At the same time, it is also evident according to Raab that, in the olfactory field, neither consistent relationships between chemical-physical characteristics of scents and their sensations are discernible, nor are there any systematic classification points according to which subjective scent qualities can be ordered (Raab 1998, p. 16). Since there is no scientifically justifiable, objective, systematic classification of odors, one must, according to Eberle, fall back on the subjective perception of people when investigating odors (Eberle 2021, p. 38). This makes it clear why the study of olfactory landscapes should be based on a phenomenological-social constructivist framework if the focus is on people's perception of them.

Thus, the understanding of olfactory landscapes presented here follows on from the previous work of Henshaw and McLean (cf. Henshaw 2014; McLean 2016, 2017, 2019, 2020; Perkins and McLean 2020). They focus on the subjective experience of the experiencing individual (Lammes et al. 2018, p. 54; McLean 2016, p. 185) and depict (and also map) the temporary perception of a space (McLean 2016, p. 185, 2017, p. 93). This view is also reflected in the cartographic preparation of the studied smellscapes, as it was further developed in the already mentioned master thesis on the olfactory landscape of Christmas and Christmas markets in particular (cf. Endreß, 2022). Thus, the smelling subject becomes the focus of olfactory perception. The perceived odor is not located at its supposed source, but with the individual himself who perceives it, because, according to Bischoff, the olfactory space exists for the perceiving subject precisely when an odor is smelled or an emotional impression is felt (Bischoff 2007, pp. 50–51). The designations of the perceived odors are also not generalized in this approach; the focus is on the direct association of the individual when perceiving the odor. This is also advantageous because, especially in the ‘Western world’, the vocabulary for describing odors is very weak and in some cases not developed at all (Bischoff 2007, p. 22; Eberle 2021, p. 35; Lammes et al. 2018, p. 63; Porteous 2019, p. 26; Strugnell and Jones 1999). In describing the smells, the subjects therefore, as Raab puts it, mostly resort to 'external' characterizations, metaphors, circumlocutions or references to the sources of the smells (Raab 1998, p. 16). For example, the smells at a Christmas market are hardly ever described with characteristics such as “Salty [or] Spicy” (Endreß 2022, p. 109). Rather, people resort to the suspected sources of odor such as cigarette, sausage or hedge (Endreß 2022, p. 109). The recourse to the actual descriptions thus enables direct mapping of the interpretation of the odors and also facilitates the communication of the results with other non-experts, as these terminologies are clearly more connectable than the specialist vocabulary of perfumers and wine connoisseurs. Further signatures were developed for the cartographic representation of the odors (see Fig. 1).

Fig. 1
figure 1

Structure of the smellscape signatures. Modified according to Endreß (2022)

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For this purpose, the basic method of representation used was that of McLean, which also partly uses concentric circles to represent odor intensity. Unlike in some of McLean's works (e.g., presented in McLean 2016) a possible effect of the wind on the distribution of the odor was not simulated, as a subsequent reconstruction of air movements on this scale would be difficult to carry out realistically (see in detail Endreß 2022, p. 47). In addition to odor intensity, which is represented by the number of concentric circles, the signatures are also colored to better convey the perceived odor to the viewer. While McLean partly draws on the color schemes of the spatial environment in her choice of colors (Lammes et al. 2018, p. 86) or determines the color choice for certain odor categories in advance (for example, perfume is always depicted as pink) (McLean 2016, p. 178) in the work discussed here the participating subjects were asked directly about their color associations. This seems to make sense, as synesthesia is a good way of expressing bodily experience (Hasse 2017, p. 355). It was noticeable that the people mainly fall back on the stereotypical color attributions of the presumed odor emitters in their choice of color (for example, the color blue is attributed to the smell of water). At the same time, it becomes apparent that food odors are mainly assigned colors in the range of brown, white, yellow, orange, and red. Gender-specific stereotypes could also be suspected in the attribution of the color purple to the smell of perfume (Endreß 2022, p. 110). Here it becomes clear why a social constructivist perspective can be particularly fruitful for the perception of smells: Socially anchored patterns of interpretation and discourse (for example, the gendered color assignment 'pink' and 'purple' for perfumes, which have feminine connotations) come to light and can be interpreted and understood in the theoretical framework used.

The biggest change in the signatures compared to previous work is the expansion of the signatures to include additional levels of information. Thus, further signatures were added for the evaluation of the odors based on the perceived sensation (pleasant to unpleasant), the perceived familiarity (new to familiar) and the perceived expectability of the odor (surprised to expected). While the first two characteristics could be completed by extending the circle signature, a signature outside the circle was chosen for the expectability, as it would otherwise be too cluttered and become confusing. Figure 2 shows the smellscape of a person at the Karlsruhe Christkindlesmarkt with the application of the developed signatures.

Fig. 2
figure 2

Perceived smellscape at the Karlsruhe Christmas Market. Modified according to Endreß (2022)

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Through consultation with the participants, it was possible to qualitatively assess the extended survey procedure (the additional characteristics also had to be surveyed). It can be seen that the persons were able to assign the odor intensity, the color, the name as well as the direct sensation well. With regard to the expectability and familiarity of the odors, however, this appeared to be more complicated, which is why it can be assumed that these characteristics should no longer be surveyed in the future (at least not in the form of a questionnaire with a five-point Likert scale undertaken here). This would reduce the overloading of the signatures (especially through the signature regarding expectability) and open up another option to use the signature used for the familiarity characteristic for other characteristics (see in detail: Endreß 2022).

5 Smellwalk Step by Step

To promote a continuous further development of the methodology around the topic of smellscapes, it seems to make sense not only to describe the further developed presentation but also to explain the procedure of a smellwalk. It should be mentioned again that the procedure described here is a methodology that has been further developed according to personal experience (see Endreß 2021, 2022; Endreß and Jutz 2022) and is fundamentally based on McLean's findings (see Perkins and McLean 2020), which represents only one of many possibilities to collect odors. Accordingly, this is my personal approach to the survey of olfactory landscapes so far.

First, the survey instruments will be discussed before the procedure of the smellwalk is described in more detail. The odor stimuli experienced must be noted during the walk. For this purpose, it is advisable to hand out a questionnaire to the participants of a smellwalk, which contains the criteria to be recorded (the questions of the questionnaire are shown in Fig. 3; only the questions which were directly related to the creation of the Smellscapes are presented. In addition, the original questionnaire was available in both English and German; only the English questionnaire is shown here).

Fig. 3
figure 3

The questionnaire used in the study of the smellscape of the Karlsruhe Christmas market. Own depiction

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Based on previous experiences, it is recommended to record the olfactory impression (what is smelled?), the intensity (how strong is the smell?), the perception of the smell (how do I perceive this smell?), a color associated with the smell (which color is associated with the smell?) as well as the location of the person (where is the smell perceived?). It turns out that the participants seem to have few problems in evaluating these criteria quickly and confidently. Of course, it is conceivable to collect further criteria, whereby a test run is recommended beforehand, since, as already mentioned, it seems that not all criteria can be collected without problems. In particular, the question about the familiarity of the odor as well as its expectability seemed to lead to slight confusion and the participants seemed to find it difficult to answer these questions, which is why these questions should no longer be asked in future surveys, or at least not in this form. While a seven-point Likert scale was used for the intensity and a five-point Likert scale for the perception of the odor, it seems sensible to choose an open answer category for the survey of the odor impression and the assigned color to do justice to the subjective character of the research object. An open response category for the type of odor also seems to make sense because especially in the 'Western world', there is so far only an insufficient and partly missing shared vocabulary in relation to odor perception (Bischoff 2007, p. 22; Eberle 2021, p. 35; Lammes et al. 2018, p. 63; Porteous 2019, p. 26; Strugnell and Jones 1999). While there is a wealth of expert knowledge in the field of odors [think, for example, of perfumers (Margolies 2006, p. 113) or wine connoisseurs and skilled olfactory researchers (Eberle 2021, pp. 36–39)] this knowledge is not something these groups have in common with the general population. By reverting to a less systematic, free text input, the level of knowledge of the average participant is thus taken into account, which also facilitates the communication of the results with non-experts (cf. Eberle 2021, p. 46). Also, a preceding training of the participants would mean an enormous expenditure of time, which, depending on the resources of the respective study, might be difficult to manage in some cases. The free text input thus enables resource-saving research by 'average noses for average noses'. The localization can of course be done using a physical map, whereby the advantage of a digital mobile device should be emphasized here. Not only does it allow for a problem-free survey in the dark, but it now mostly has a simple and relatively accurate location function (although this should be checked beforehand). In addition, the use of a mobile device should now be familiar enough for a large part of the population to base such a research project on it.

Now that the survey instruments have been presented, the procedure of a smellwalk will be discussed. A survey in groups seems to make sense, as more information can be collected, and larger spaces can be surveyed. In addition, a larger number of participants increases the likelihood of differing perceptions and patterns of interpretation, which can contribute to a deeper understanding of the object of research (Perkins and McLean 2020, p. 162). My surveys so far have always taken place in small groups (up to five people), which has several advantages: On the one hand, it shows that there are frequent questions, which are easier to handle in smaller groups. Furthermore, it offers the advantage of keeping a better overview of the group. Since I prefer a very free approach (relatively loose directions), so that the participants can freely 'follow their nose', the small groups make it possible to remain approachable to all persons, since the spatial distance between the 'smell researcher' and the participants remains relatively small. Before starting the smellwalk, a detailed introduction to the topic should take place. The questionnaire should be explained and all relevant questions clarified. Furthermore, it seems useful to briefly introduce the participants to intensive smelling, which Eberle calls sniffing (Eberle 2021, p. 35). This enables better odor perception, as more molecules pass through the olfactory cleft to the olfactory mucosa (Hatt and Dee 2009, p. 47). In addition to this short sniffing course, it should also be emphasized that the participants should only discuss perceived odors after they have already noted them down to exclude mutual influence (one is then often surprised how excited the participants want to chat about the smells). Finally, the intended route or the prescribed investigation space should be defined so that the different results actually cover the same physical spaces. Depending on the preferred procedure, the person in charge can then accompany the participants on the smellwalk or be available at a central location for questions. It has been shown that the duration of a smellwalk should be limited. Already after a few minutes, the participants showed the first signs of fatigue in the previous studies, which is why short 'breathers' were taken. Active smelling seems to be quite demanding, possibly also because we rarely use it in everyday life, which is why a total duration of about 30–45 min per Smellwalk (with breaks) can be recommended. At the end of the Smellwalk it seems to make sense to have a final discussion with the participants. This can be done in the group as well as in individual conversations. This provides further interesting insights into the perception of smells. In particular, these discussions help to evaluate problems in the chosen survey form. In the project presented here, for example, it became clear through the final discussions that it was sometimes complicated for the participants to assign the expectability and familiarity of odors, and that it was often mentioned with surprise that short breaks had been necessary in order to concentrate on smelling again (a subsequent look at the data underlined these impressions of the participants). Furthermore, these discussions, according to experience, also motivate the olfactory researcher himself, as there is often positive and surprised feedback from the participants (it is not uncommon to hear sentences like: ‘I have never actively tried to sniff my world before and I am surprised how differently I perceived everything’).

6 Conclusion

The study of olfactory landscapes presents us with new challenges. The basics of their collection, representation, and interpretation are currently in an experimental phase and I hope that this article can contribute another building block to this discussion. Furthermore, it seems extremely important to include the theoretical dimension more strongly in this discourse in addition to these 'practical' discussions. The question of how and why we survey olfactory landscapes can only be meaningfully debated if we place these considerations on a theoretical foundation. It turns out that the understanding that olfactory landscapes are social constructs that emerge against the backdrop of social norms, assumptions, discourses, and personal impressions also influences the way we represent these landscapes. The best example of this is probably the location of smell. Instead of locating the ‘actual source of the smell’, the central point of experience becomes the person themselves. The old question of whether a tree, if it falls in the forest and no one is there to hear it, still makes a sound, is the acoustic counterpart to this. Does a rubbish bin smell strongly of rubbish when no one is there to sniff it? From our phenomenological point of view, the focus is on the experience of the smell and thus on the smeller himself. However, if he does smell the rubbish bin, he does not smell an essential rubbish smell of the rubbish bin but a complex bouquet of smells, which he constructs into the ‘rubbish bin smell’ on the basis of his social background and his personal experience. Therefore, the theoretical positioning of olfactory landscapes in a phenomenological-social constructivist context made here makes it possible to theoretically justify the chosen way of mapping and surveying the smellscapes. The mapping itself remains strongly in the phenomenological realm. The location of the smell, the assigned color as well as the description or naming of the smell seems to be deeply individual at first. At the same time, it is possible to derive social patterns of interpretation of odors and olfactory landscapes from these many experiences: Which smells do we associate with which colors, possibly on the basis of social norms? Why are some smells read as feminine, others as masculine?

Thus, the understanding of smellscapes or their construction presented here expands the possibilities of interpretation of the results obtained by smellwalks or other odor-related survey methods. Smellscapes thus not only depict the olfactory backdrop of a space but much more open up the discussion of the socialization of the emerging patterns of interpretation. In doing so, we lift the discussion from the purely phenomenological level, in which the personal experience of an odor is in the foreground, to the societal level: What patterns of interpretation and discourse of odors are present in different (sub-)societies? How do these patterns emerge? What effects do these have on the construction of a space itself? Finally, reference should be made once again to Raab (1998), who had already taken up this approach early on, even if not directly in relation to smellscapes.

The extended representation method of the smellscapes presented here can help us to show these patterns and to put them into context. Through the increased information content (finally, up to six different types of information (type of odor, intensity, sensation, familiarity, expectability, and associated color) can be represented by the approach presented here) we move away from a purely descriptive level of odors and deal more with their (subjective) interpretation and perception. These representations thus allow us to pick up on the actual lived space and make it communicable. Thereby, the approach presented here offers a variety of possibilities to represent it: As already mentioned, the questioning about familiarity and expectability delivered rather unsatisfactory results, which is why these factors can be replaced by other information. This raises the question of further information that can be collected during smellwalks. For example, it could be asked whether this smell is perceived as 'fitting' or 'not fitting' to the environment, i.e., the smellscape found here (in this case the smellscape of a Christmas market). This would provide further insights into odor stereotypes.

In addition, the question naturally continues to arise as to how the possibilities for representing olfactory phenomena might develop in the future. Here, a look back at audiovisual maps raises the question of whether it might not also be possible to reproduce odors directly, instead of merely reflecting them indirectly via visually perceptible symbols. Attempts to this end have at least already been made (although not always directly in a scientific context): With the advent of color film, some film studios and cinema owners saw fit to expand the film experience to include the olfactory level (Niedenthal 2012; Spence 2020). In the field of video games, too, there have been repeated attempts to incorporate an olfactory layer (Niedenthal 2012). In retrospect, these attempts can be seen as having failed. However, with the constant technological development, new possibilities are now coming to light for (digitally) representing or reproducing smells. One example is the app-controlled ‘Vocktail’, a glass (filled with water) that simulates different flavors with the help of electronic stimuli (Kerruish 2019). Also, the attempt to send smells similar to text and audio messages has been made several times (although quite unsuccessfully) (Twilley 2016). At the same time, game studios continue to try to integrate smells into the gaming experience. Especially in the field of augmented and virtual reality, efforts are currently being made to reproduce smells directly (Kerruish 2019). The extension to the olfactory level seems to let us experience what we perceive more intensively (cf. Flavián et al. 2021). In the meantime, the olfactory level is also occasionally included in direct research on possible representational possibilities of spaces (cf. Dodt et al. 2017; Edler et al. 2018, pp. 250–251).

At the same time, however, other (less technical and more critical) questions are raised: Can Smellscapes be suitably explained by a theory that derives from social constructivist landscape research, where the focus is mainly on visual stimuli? Does the apparently different processing of olfactory impressions in the brain (the lack of regulation by the thalamus) have an effect on our theoretical framework (are there, for example, ‘essentially bad’ odors after all?)? How effective is the almost ironic attempt to represent olfactory experiences on a visual map? All this must be discussed, expanded and, if necessary, discarded in further work.

And as long as we find ourselves in this 'darkness' of uncertainty, there is probably only one thing left to do: to follow our nose.