Sustainable Tourism: A Human-Centered Approach

The aim of this paper is to present an alternative approach to sustainable tourism-derived from the human-centered angle. In line with this assumption, when considering the principles of sustainable tourism, the opinions of all groups of tourism actors, including host communities, tourists and tourism businesses should be taken into account equally with other factors, not merely as one of many decision makers, but as the main frame of reference. The research methodology is twofold. As regards the theoretical foundation, the model approach has been applied to conceptualize the intra-generational and inter-generational perspectives upon tourism sustainability. Consequently, the former is concerned with the problem of internal sustainability connected with the advantages achieved and disadvantages borne by tourism actors. The inter-generational perspective, on the other hand, is related to the problem of long-term tourism development under conditions of internal sustainability. In the empirical part of the research, the model was applied in a survey carried out in seven chosen areas in Poland. To this end, a set of auxiliary tools (an adopted Likert scale and a working matrix) was developed and positively tested in real-life conditions. The novelty of the study as a whole consists in the fact that it postulates taking into consideration the ‘human-centered perspective’ related to all groups of tourism actors, including who are not directly involved in


Introduction
The notion of sustainable tourism undoubtedly refers to a wider concept of sustainable development [1][2][3][4][5][6], which in the most general sense stresses the need for rational management of natural, socio-economic and cultural resources [7]. In tourism studies, concepts related to the principles of sustainable development began to appear on a larger scale in the mid-1980s. It should, however, be noted that as early as 1965, Hetzer formulated the term responsible tourism, which was very close to the contemporary principles of sustainable tourism [8,9]. Nevertheless, the deeper discussion about new ways of developing tourism started with the concept of alternative tourism proposed by Krippendorf [9]. As the term 'alternative' suggests, its idea was conceived in opposition to 'mass' tourism, which was mostly considered as the 'bad option' in relation to small-scale, 'alternative' tourism, treated as the 'good option' [5,[10][11][12][13][14]. At the same time, scholars began to coin other similar attributes of tourism, such as: angepasst Tourismus, appropriate tourism, discreet tourism, ecoethnotourism, ecotourism, environmentally-friendly, environmentally-sensible, green tourism, tourisme vert, nature-based, naturnähe Tourismus, soft tourism, saufer Tourismus [15,16]. Their meanings were in majority relatively close to the contemporary understanding of the concept of sustainable tourism, regarded as the most desirable way of developing tourism activity. Consequently, many authors adopted an evaluative approach and juxtaposed the 'new' forms of tourism with the 'old' ones, by which they usually meant mass tourism [17,18]. In this context, Lane [19] used the term 'sustainable tourism' to distinguish the rules, legal regulations and methods of management that determine development of tourism in areas of high natural or cultural merits in need of protection. Forsyth [20] similarly emphasized that sustainable tourism could not cause harm to the natural and cultural environments.
A broad overview of definitions of sustainable tourism was presented among others by Butler [21] and (in the Polish literature) by Kowalczyk [22]. This first author was particularly skeptical towards the view that sustainable tourism can be treated as a panacea for all the problems of contemporary tourism and, consequently, presented his own view on the meaning of sustainability in this matter. In particular, he claimed that sustainable tourism could be seen in two ways [23,24]. Firstly, it could be approached from the semantic side, interpreting the feature of sustainability as a guarantee of a long-term survival on the market. The second way was concerned with issues of development of destination areas without breaking the principles of sustainable development. Butler's view about the ambiguity inherent in the understanding of the term 'sustainable tourism' was supported by Niezgoda [25], who claimed that this concept had appeared as a result of research on interrelations between tourism, environment and development. According to this author, sustainable tourism was treated either as a tool for the realization of sustainable development or for the development of tourism itself. Another approach was presented by Butowski, Makowska-Iskierka and Pokojski [26], and Butowski [1], who proposed applying the concept of sustainable tourism to measure the tourism development of destination areas. Finally, the skeptical opinion of Mika [27,28] should be mentioned. This author claims that the idea of sustainable tourism is not an effective alternative for overcoming the neoliberal growth paradigms that prevail in the contemporary development policies.
Apart from the broad discussion of the theoretical foundations of sustainable tourism which has been carried out in academia for last decades, official documents of declarative or quasi-normative character have also been issued by international organizations. Some of them, such as: the 'Charter for Sustainable Tourism' [29], 'Agenda 21 for the Travel and Tourism Industry: Towards Environmentally Sustainable Development' [30], 'Global Code of Ethics for Tourism' [31], 'Sustainable development of tourism. Conceptual definitions' [32] and Global Sustainable Tourism Criteria [33] deserve special recognition. The list should be completed with a guidebook entitled 'Indicators of Sustainable Development for Tourism Destinations' [34] issued by UN World Tourism Organization.
Taking into account the results of the discussion on the issue of sustainability of tourism, which is still far from final conclusions, the purpose of this paper has been formulated as the furthering of the investigation into sustainable tourism by applying an alternative approach, deriving from a human-centered perspective as the main frame of reference.
The problem is specified through the adoption of the main hypothesis, according to which, paradoxically, in the discussion of sustainable tourism development, the voices of all involved actors are not taken into account equally. This applies primarily to local communities who host tourists. This group, often internally diverse, has no strength to oppose the external pressure. This pressure comes, on the one hand, from various public and private organizations striving to impose unacceptable norms concerning, in the first place, protection of the natural environment, and, on the other hand, from powerful tourist operators aiming to exploit the local resources for their own benefit. As a result, many local communities find themselves between a rock and a hard place, which results in the decrease of their life quality. This pertains in particular to those representatives of local communities who are not directly involved in tourism development in the area where they live. Thus, they do not have a share in any of the benefits, while all too often they bear the aforementioned socio-cultural, economic and environmental costs. For the purposes of this publication, this group has been dubbed 'the weakest link'. It is the author's view that the level of fulfilment of the needs of this group together with the costs they bear should set the boundary between the states of sustainability or unsustainability of tourism in the given region. The problem has already been recognized quite a long time ago, however usually not in the context of sustainable tourism development, but rather as part of the broadly discussed phenomenon of overtourism, not only in the context of environmental justice, but also social justice [35][36][37].
In order to verify or falsify such a hypothesis, it is necessary to define how the very idea of sustainable tourism is understood in the context of the outlined problem and research goal. To this end, an original model of sustainable tourism is proposed. It attempts to take into account the main theoretical premise of sustainability, which concerns the rational management of existing (natural, socio-cultural and economic) resources in the meeting of people's needs. This premise is considered in the proposed model of sustainable tourism from an intra-generational and an inter-generational perspective. The former assumes the achievement of at least a minimal level of expected advantages gained from tourism by all groups of tourism actors, while not exceeding the maximal acceptable level of disadvantages generated by this activity (Figure 1). It is necessary to underline that it is tourism actors who, as a whole, are the subjects of the process of sustainable tourism development in given areas. At the same time, they can be sub-divided into two main groups: tourists and local communities, who often have conflicting needs, at least in the short-term perspective. Additionally, even within these two main groups of tourism actors, one can distinguish various, often significantly different, expectations and priorities. All the aforementioned aspects should be taken into account when discussing the minimal expected level of advantages gained and the maximal level of disadvantages experienced by the various subgroups of tourism actors. To illustrate this theoretical assumption, the 'weakest link' principle can be applied. As mentioned before, it especially concerns those parties within local communities who are not directly involved in tourism activity, so they achieve relatively low advantages (if any), at the same time often experiencing the greatest disadvantages connected with this activity.  [1,26] Changed. ADmin-the minimal acceptable level of advantages expected by tourism stakeholders; ADmax-the maximal level of advantages gained by tourism stakeholders; DisADmax-maximal level of disadvantages, which tourism stakeholders are ready to bear.
Taking into account the aforementioned assumptions it is possible to define the theoretical conditions for sustainability of tourism as well as its unsustainability in the segments of advantages and disadvantages. They can be represented by the following formulas: This includes two conditions: (a) Real advantages (ADreal) should (at least) achieve or cross the level of minimal expected advantages (ADmin); and (b) Real disadvantages (DisADreal) should be below (or at most) equal the maximal level of acceptable disadvantages (DisADmax).
These conditions correspond to the area ABF on the model graph; they represent the state of sustainability (in both segments: advantages and disadvantages).
This includes two conditions: (a) Real advantages (ADreal) do not achieve the level of minimal expected advantages (ADmin); and (b) Real disadvantages (DisADreal) are below (or at most) equal the maximal level of acceptable disadvantages (DisADmax).
These conditions correspond to the area OAFE on the model graph, and represent the unsustainability in the segment of advantages while meeting the conditions for sustainability in the segment of disadvantages.
This includes two conditions: (a) Real disadvantages (DiSADreal) cross the level of maximal accepted disadvantages (DisADmax); and (b) Real advantages (ADreal) (at least) achieve or cross the level of minimal expected advantages (ADmin).
These conditions correspond to the area BCF on the model graph, and represent the unsustainability in the segment of disadvantages while meeting the conditions for sustainability in the segment of advantages.
This includes two conditions: (a) Real advantages (ADreal) do not achieve the minimal expected level of advantages (ADmin); and (b) Real disadvantages (DiSADreal) cross the level of maximal acceptable disadvantages (DiSADmax).
These conditions correspond to the area CDEF on the model graph; they represent the state of unsustainability in both segments (advantages and disadvantages).
The inter-generational perspective, on the other hand, is related to the problem of longterm tourism development under conditions of internal sustainability, as shown in Figure 1. In both perspectives the advantages and disadvantages of tourism should be understood as broadly as possible, including social, cultural, economic and environmental benefits and costs. According to the adopted conditions of the intra-generational frame of reference, determined in Formulas (1)-(4), the above-mentioned idea of sustainability should be related to the long-term, inter-generational perspective. It has been illustrated in Figure 2, where an example of hypothetical state of unsustainability passing into sustainability has been presented.
The novelty of the afore-presented model approach is that it has been rarely used in the discussion on the principles of sustainable development, including sustainability in tourism. On the contrary, an overview of the literature in question shows that the attention of the authors was primarily focused on descriptive presentations of various aspects of sustainability, with particular emphasis on the idea, the origins and the evolution of the phenomenon as well as terminological issues related to it [16]. Still, some attempts to address this subject in model terms too have been made, for example Niezgoda's [25] concept of the evolution of the idea of sustainable tourism, or Weaver's [13] proposition to treat sustainability and unsustainability as the extremes of a two-directional continuum.

Materials and Methods
The aforementioned assumptions of sustainability in the intra-generational perspective presented in the model of sustainable tourism ( Figure 1) have been applied in an empirical part of the study not only for testing the adopted working hypothesis but also for the examination of the model itself, as an original research tool. It required the preparation of appropriate auxiliary tools for the model. They consisted of a calibrated (with an adopted 10-point scale) working matrix (Figure 3), and a 10-point scale (consisting of a pair of two 5-point Likert scales). In Figure 3, • quarter A corresponds to the area OAFE in the model graph, representing unsustainability in the segment of advantages of tourism (sustainability in disadvantages); • quarter B corresponds to the area ABF in the model graph, representing the state of sustainability in advantages and disadvantages of tourism; • quarter C corresponds to the area BCF in the model graph, representing unsustainability in the segment of disadvantages of tourism (sustainability in advantages); • quarter D corresponds to the area CDEF in the model graph, representing unsustainability in both segments: advantages and disadvantages of tourism.
The working matrix also contains specific points, which can be applied for more detailed analyses: The working matrix should be calibrated according to the adopted scale. For the purpose of this study, a 10-point scale was used to measure the level of the respondents' satisfaction (advantages) and dissatisfaction (disadvantages) in the context of tourism sustainability and unsustainability. The scale actually consists of a pair of two 5-point Likert scales, which measure the levels of sustainability and unsustainability in advantages and disadvantages of tourism treated independently. The border line separating sustainability and unsustainability passes between the values 5 and 6, as presented in Figure 4. The matrix also enabled further processing of the data (with sufficient accuracy), including the calculation of average values of individual ratings as well as the measurement of vector distances from points a, b, c and d. The applied scale together with the working matrix made it also possible to present the results precisely in a graphic form. Finally, it should be mentioned that one of the immediate purposes of this study was the testing of the model of sustainable tourism (together with its auxiliary tools) in empirical conditions. The field research was carried out in 2015-2019, in seven Polish tourist towns, five of which were located on the Baltic Sea coast or in its vicinity ( Table 1). The respondents consisted of two main groups (similar in terms of numbers): tourists and the local community. The sample was non-representative but with acceptable validity to test both tools (the working matrix calibrated to the adopted scale).

Results
Selected results of the survey have been presented in Table 2. They contain the average values of advantages and disadvantages calculated on the basis of individual ratings given by all the respondents (including two main groups: representatives of tourists and local communities) in particular towns. The presented data point to the fact that tourism was assessed as sustainable in majority of towns. This is substantiated by the average values of advantages. They all exceeded the border value of 5 (separating unsustainability from sustainability). As regards disadvantages, only one town (Inowłódz) slightly exceeded the border value of 5, separating sustainability from unsustainability. Source: [26] Changed. Now, the calculation of the vector distances from individual predefined theoretical points a, b, c and d has enabled a detailed analysis of the situation of individual towns. Thus, the vector distance from point b (the smaller the better) indicates to what extent the real position of the given town departs from the theoretically most advantageous situation of maximum sustainability. The vector distances from points a, c and d, in turn (the greater the better) indicate how far the given locality is placed from the theoretical points of maximum unsustainability in the segments of: advantages (distance from point a), disadvantages (distance from point c) and advantages and disadvantages combined (distance from point d). The vector distances provided in Tables 3 and 4 should be understood and interpreted in the same way.  Transposing the aforementioned numbers (Table 2) into the working matrix one can graphically present the positions of the particular towns. Five of them are located in the quarter B, that is, the one which corresponds to the state of sustainability in relation to the advantages achieved and disadvantages borne by tourism actors. Only the town of Jastarnia has just been positioned in the border line separating the acceptable and unacceptable disadvantages, and Inowłódz slightly exceeded this line ( Figure 5). In addition, it is worth stressing that the application of both tools allowed the author to carry out more detailed analyses. Despite the fact that five of seven towns were positioned in the sustainable quarter B, it is possible to note quite distinctive differences between them. As shown in Figure 5, the most advantageous position seems to be occupied by the town of Hel. It is reflected in the shortest vector distance between its location and the point b (representing the highest theoretical level of sustainability), which also accords with the most favorable assessments ratio (8.8 point of advantages in relation to 2.7 point of disadvantages). The opposite position is held by Węgorzewo, where the assessments ratio was 5.9 (advantages) in relation to 4.7 (disadvantages). As mentioned before, the applied method also made it possible to carry out more detailed analyses regarding the positions of the particular towns in relation to points a, c and d (as defined above). This is particularly noticeable when it comes to the positions of Inowłódz and Jastarnia. Both of them received quite positive assessments of advantages (respectively: 7.8 and 8.6) but at the same time their ratings in relation to disadvantages were relatively high (respectively 5.2 and 5.0), just exceeding or equal the border value (in the adopted scale) separating sustainability from unsustainability in the segment of disadvantages. Such high assessments of disadvantages in Inowłódz ensured that this town was located in the unsustainable quarter C.
The aforementioned results concern the opinions of all the respondents in the particular towns, but similar analyses can be carried out comparing tourists and local communities. The results of such exemplary analyses have been presented in Tables 3 and 4, which break down the opinions of tourists' and local communities' representatives per individual towns.
When comparing the opinions expressed by the tourists' representatives (Table 3) and local communities (Table 4), a slight difference is visible, namely the ratio in the segment of advantages is 8.0 (the average value for tourists) to 7.8 (the average value for local communities), while in the segment of disadvantages, it is 4.2 to 4.1 (respectively). This means that on average, in all the towns, the tourists' representatives rated the advantages gained from tourism higher than the local communities' representatives, but they also pointed to slightly bigger disadvantages related to tourism. Be that as it may, more accurate and applicable conclusions may be drawn when comparing the measured opinions of tourists and local communities separately for individual towns.
Additionally, the applied tools enabled more detailed analyses of the internal differentiation of the opinions, especially within the rather heterogeneous group of local communities. To illustrate this possibility, Figure 6 presents the results concerning the local communities broken down into three subgroups: local authorities and non-governmental organizations (NGOs), tourist businesses, and local inhabitants not involved in tourism. It is clear that they occupy different positions in the working matrix, even though all of them are located in the sustainable quarter B. Analyzing their positions, one can observe a characteristic feature that the level of sustainability was rated the highest by the representatives of the local authorities and NGOs, followed by tourist businesses; the lowest assessments, on the other hand, were associated with the inhabitants who were not directly involved in tourism activity. This situation corresponds to the aforementioned 'weakest link' principle. It stresses the requirement to take into account, when talking about sustainability of tourism development, the opinions of locals who are not involved in tourism, as it turns out that they are the weakest link. Consequently, under the proposed conditions of sustainability, their opinions should determine the minimal expected level of advantages and the maximal acceptable level of disadvantages.

Discussion and Conclusions
As indicated in the introduction, the main purpose of the paper was to present an alternative approach to tourism sustainability, adopting a human-centered perspective as the main frame of reference. The reason for such a formulation of the purpose was connected with the author's belief that this perspective is not sufficiently represented in the discussion about the issue of tourism sustainability. It is especially visible in relation to host communities, which inhabit not only remote areas of 'exotic' islands, but also 'peripheries' in relatively well-developed countries. They are often too weak to oppose not only neoliberal economic policies, but, paradoxically, also the paradigm of sustainable development which puts environmental issues at the fore (too often at the expense of socio-cultural and economic local aspects). The rules of this paradigm are often imposed by the national governments and international organizations on the host communities, disregarding their real needs and local conditions.
Taking into account these facts, a different approach to tourism sustainability has been proposed. It aims to bring the views of various groups of local communities to the fore and take them seriously into account when talking about the paths of tourism development in their areas. Such an assumption underlies the construction of the sustainable tourism model (based on previous author's proposals, presented in: [1,26]), with the exposed intragenerational perspective, presented in this paper. The model presumes that the decisions on the (social, environmental, economic) costs borne and the advantages achieved in connection with tourism should be made primarily by (broadly understood) host communities, taking into account the opinions of tourists who visit their areas. Those parties should (as much as possible) have the right to set the maximal level of disadvantages acceptable to them together with the minimal level of advantages generated by tourism which they expect. Importantly, these levels should be determined through an internal compromise, taking into account also the opinions of those groups of local communities that do not benefit from tourism but bear the costs of its development (the 'weakest link' principle). Finally, when discussing the model assumptions, it is worth noting that the limitation of the afore-mentioned rights assigned to all tourism actors should be determined by the law in force in the given areas. At the same time, it is quite obvious that tourism actors should be involved in the process of law-making to the greatest extent possible.
As regards the axiological foundations, the principles of the proposed model of sustainable tourism refer to the views presented by Pope Francis in his famous encyclical letter "Laudato Si'" [38]. In this document the recommended attitude of man to the natural world is dictated by the biblical verse "The Lord God took the man and put him in the Garden of Eden to work it and take care of it" [39]. In the context of this paper, it is also worth mentioning John Paul II's Message for the 23rd World Day of Tourism in 2002, where the following claim was formulated "We should favour forms of tourism that show greater respect for the environment, greater moderation in their use of natural resources and greater solidarity with local cultures" [40].
Furthermore, the proposed model is related theoretically to the concepts of carrying capacity [41] and the limits of acceptable changes [42]. However, unlike in the source concepts, emphasis is put on local tourism actors as the subjects of the entire development process. In the first place, it is the local community who has the right to define the boundaries of acceptable changes (carrying capacities) occurring in their areas. These boundaries can be easily transposed into the model rules determining the theoretical areas of sustainability and unsustainability. The proposed model is also related to Butler's famous theory of tourism area life cycle [43]. This is evidenced by the possibility of referring particular stages of the evolution of tourist areas to the model states of sustainability or unsustainability. In the proposed model of sustainable tourism, however, the time factor as an independent variable plays an important role only in the long term (inter-generational) perspective (as illustrated in Figure 2). As regards the intra-generational perspective, on the other hand, the relations between advantages and disadvantages of tourism are considered at the given moment of time (Figure 1), so it is not treated as a factor.
It is worth mentioning that the proposed approach can be applied as a counterweight to numerous quantified index methods [34] with their standards and norms imposed by external institutions. Unfortunately, all too often they do not devote sufficient attention to the specific local economic and socio-cultural circumstances. In this context, the proposed method can also be used as a tool for verification of the actual level of satisfaction of all tourism stakeholders (taking into account their 'weakest link') in the light of the implemented sustainable development policies. This does not mean that we have to abandon the various index methods and replace them entirely with the 'subjective' assessment carried out by the local community and tourists. On the contrary, it would appear that the optimal solution for planning sustainable tourism would be the use of both mutually verifiable approaches, including mostly quantified 'objective' methods and their 'subjective' reception by all tourism stakeholders (actors) in the given areas.
Last but not least, it seems quite clear that the proposed model can be used not only for sustainable tourism, but also for other areas of human activity in the context of sustainable development [44][45][46].
Apart from the presentation of the theoretical foundations of the proposed model, the paper also had a more practical purpose, namely that it was concerned with the possibility of applying the adopted human-centered principles of sustainable tourism in empirical research. In this context, the main difficulty was how to measure, process and transfer subjective opinions of various groups of tourism actors into more quantifiable and comparable data. This transposition was also necessary for the determination of the situations of the particular towns in relation to the adopted principles of sustainability and unsustainability on the basis of the respondents' answers. To solve this problem, a set of auxiliary tools was developed and applied in real survey conditions. It consisted of a working matrix calibrated in accordance with the adopted measuring scale. The scale consisted in fact of a pair of 5-point Likert's scales [47], which allowed the rating of the respondents' subjective opinions on sustainability and unsustainability. However, it is worth noting that this tool, constructed specifically for the present study, could most likely be replaced by other techniques enabling similar measurements. Despite this fact, the obtained results of the field research can be considered acceptable, especially with regard to the tested working tools. They turned out to be sufficiently accurate and, at the same time, easy to conduct among various groups of respondents. The applied working matrix also enabled the analysis of the processed data, as well the presentation of the results in a clear and convenient manner.