**1. Introduction**

The growth of the human population enhances the extensive use and consumption of materials, while the existing lifestyle and established consumer patterns lead the planet and its population to an unstable situation without possible reversal [1]. In other words, the rate of use and consumption of resources and material, especially in developed countries, cannot be maintained without causing significant damage to the environment, society, and economy. Therefore, keeping anthropogenic systems sustainable is of crucial importance; but how do we define, maintain, and finally measure sustainability?

According to Graymore et al. [2], "sustainability is an essential goal for planning and natural resource management at all spatial scales", as it requires the population to live within the limits of the supporting systems, ensuring equitable sharing of resources and opportunities for this and future generations [3].

Moreover, the measurement and the assessment of sustainability is a particularly complex process due to the wide range of issues and the complexity of the systems involved. As mentioned by Gasparatos et al. [4], ''the sustainability assessment does the difficult job to discover, study and suggest solutions for a large and heterogeneous set of issues that concern the stakeholders and extend to different spatial and temporal scales".

According to Ness et al. [5], "The purpose of sustainability assessment is to provide decision-makers with an evaluation of global to local integrated nature-society systems in short and long term perspectives in order to assist them to determine which actions should or should not be taken in an attempt to make society sustainable". It is clear from the above definition that sustainability assessment mainly evolves as a decision-making tool [6].

During the last decades, strategic planning and natural resource management are increasingly attempted at anthropogenic spatial entity scale, which refers to the spatial scale below a nation and usually includes a province or a municipality or parts of them that are under a specific management scheme or other specific authority (ex. National park). This spatial scale is the most appropriate for this purpose as it is "at this scale where ecological functioning and human activities most intensely interact" [7] and "the governance for planning, coordinating and assessing actions towards sustainable development" is effective at the specific scale [8].

There are hundreds of sustainability assessment methods [9]. Several studies [4,5,9–14] have attempted to summarize relevant methods. However, "we are still far from agreeing on how to define, plan and measure the progress towards sustainability" [10].

Most of the terms of sustainability are associated principally with the environment [15], since environmental protection is essential for sustainable development [16]. Therefore, the environmental aspects of sustainability are at the forefront [14], and the concept of environmental sustainability assessment integrates the environmental component in the decision-making process, providing deeper and more formalized knowledge [13]. Angelakoglou and Gaidajis [14] define an environmental sustainability assessment method as "a method which can provide quantitative information that can potentially help to assess the environmental sustainability".

Considering the above, a literature review of available sustainability assessment methods at anthropogenic spatial entity scale was implemented by the authors of this article, in order to assess the methods' adequacy. The literature reviews include (1) the methodology of the review and a brief description of the selected methods, (2) the criteria of the assessment and the reasoning behind their selection, and finally (3) the results of the methods' assessment.

#### **2. Methodology of Literature Search**

The literature search was implemented utilizing appropriate keywords relevant to the notions of sustainability, sustainability assessment, regional/local environmental sustainability assessment, etc., to specific search engines. As a result, articles with similar themes that had been published in international scientific journals were selected.

The methods emerged from the initial "filtering process" were thoroughly analyzed. Due to the wide range of the particular research area, a set of exclusion criteria was set and several methods were eliminated based on these criteria. In Table 1, the exclusion criteria and the excluded methods are summarized.




**Table 1.** *Cont.*

To sum up the above, from a list of sixty-one (61) examined methods that assess environmental sustainability of a spatial entity with anthropogenic activities, forty-eight (48) were excluded and thirteen (13) methods were finally selected (Table 3). Although not exhaustive, this list is, in the authors' opinion, extremely satisfactory.

In order to facilitate their analysis, the thirteen selected methods were classified based on their particular characteristics and their basic idea in four (4) categories, namely, "Indicators/Indices", "Resource Availability Assessment", "Material and Energy Flow Analysis", and "Life-Cycle Assessment" (see Table 3). The specific categorization is based on the categorization proposed by Angelakoglou and Gaidajis [14] and is widely acceptable in the economic sectors [24].


**Table 2.** The categorization of the selected methods and their brief description.


**Table 3.** The categorization of the selected methods and their brief description.

#### **3. Assessment of Selected Methods**

The scope of the evaluation of the selected 13 methods is the selection of the most appropriate method for assessing the environmental sustainability of anthropogenic spatial entities. Furthermore, the evaluation aims to document whether there is a necessity to develop new methods (or/and improving the available ones). Within that framework, the thirteen (13) methods, mentioned above, were assessed using predefined evaluation criteria.

Each method has specific advantages and disadvantages associated with its particular characteristics. However, the general features that an efficient method of evaluating sustainability must, as described (a) in the literature [4,24,40], (b) in the definition of sustainability, and (c) as defined by the requirements of the end-user, i.e., addressing issues related to its applicability and usability [2], do the following [14]:


Therefore, based on the above characteristics that a sustainability assessment method should have, five criteria listed in Table 4 were selected to evaluate the 13 methods selected. More specifically, the methods were evaluated with the application of a zero to three scale, where zero indicates the minimum and three the maximum satisfaction of the criterion. For each criterion, three questions were developed based on the characteristics previously mentioned. If the examined method satisfies the issue raised by the question (answer to the question "Yes"), then it receives one point. Alternatively, no point is attributed to the method (answer to the question 'No'). Therefore, the maximum score

for each method can be 15 points (five criteria and three questions for each criterion). Higher score implies higher satisfaction of all evaluation criteria, and consequently higher suitability for assessing environmental sustainability.

At this point, it should be mentioned that the authors recognize a certain degree of subjectivity in the evaluation process, as the satisfaction of the criteria for each of the 13 methods was judged not by a focus group but according to the analysis of the methods made by the authors and the corresponding literature [2], which referred to similar criteria for evaluating a subset of the specific methods. Among the future objectives of the authors is the more objective evaluation of the aforementioned methods with the assistance of an experts group.

#### **4. Results and Discussion**

The evaluation of the methods is presented in detail in Table 4.

The methods belonging to the Second Category, i.e., "Resource Availability Assessment Methods", exhibit the highest average score in terms of satisfaction of all the evaluation criteria (11 points out of the maximum 15 points). More specifically, the Method 2.1 "Ecological Footprint (EF)" of the Second Category of Methods exhibits the highest degree of satisfaction for all criteria (13 points out of the maximum 15 points), followed by the Method 2.3 "Wellbeing Assessment (WA)" of the same Category (11/15), the Method 1.1 "Sustainable Development Indicator Method", and the Method 1.4 "Quality of Life" of the First Category of Methods. The EF method was the highest rated method with a total score of 13/15. Particularly, the Ecological Footprint has the ability to assess environmental sustainability holistically (Criterion 1 score: 3/3), is easy to use (Criterion 4 score: 3/3), and integrates spatial and temporal characteristics of the anthropogenic spatial entity under study (Criterion 5 score: 3/3). All Methods of Category 2 satisfy to a maximum degree Criterion 5 (''Integration of spatial/temporal characteristics") and extremely well Criterion 1 (''Ability to access environmental sustainability holistically"), satisfying therefore the spatial and temporal expansion of assessment and the holistic approach of the assessment.

The assessment of all categories and methods identified some issues that need improvement, such as the ability of methods to incorporate new activities within the environmental boundaries of the anthropogenic spatial entity under study (Q.2.2: Score 0). Moreover, few methods include specific thresholds in order to evaluate quantitatively whether the performance is sustainable (Q.3.2.: Score 4).

An ideal method of evaluating sustainability should take into account all the parameters simultaneously [5]. However, the development of such a method, due to the nature of the concept of sustainability, involves a high degree of complexity, which in the case of anthropogenic spatial entities translates into high costs and time.

A new methodological framework in assessing environmental sustainability for spatial entities with anthropogenic activities that will be able to take advantages of the existing methods and deal with their challenges and their drawbacks should be developed. The scope of the framework will be to constitute a tool of particular importance for the decision-making process at the local level [14,17], giving answers to the issues highlighted above.


**Table**


*Sustainability* **2020**, *12*, 2680



*Sustainability* **2020**, *12*, 2680

#### **5. Conclusions**

The scope of this article is to summarize and evaluate the available methods for assessing the environmental sustainability of spatial entities with anthropogenic activities (for example, municipalities, regions, protected areas, and national parks). To achieve this, a literature search of existing methods for assessing the environmental sustainability of anthropogenic spatial entities was carried out. From the total of 61 methods that were found and reviewed, 48 were excluded based on specific exclusion criteria related to the proven quality of the references, the ability to simultaneously evaluate different issues of anthropogenic activity, the holistic evaluation at local level, and the focus on the sustainable aspect of environmental performance.

The 13 finally selected methods were classified according to their particular characteristics into categories, and the methods were evaluated with specific criteria such as the ability to holistically assess environmental sustainability, the ability to support the decision-making process, the ability to perform benchmarking, the applicability and ease of use, and the integration of spatial and temporal characteristics of the entity under study.

The evaluation of available methods, based on the above criteria, indicated that the methods of the "Resource Availability Assessment" category satisfy to a significant extent all the criteria set, whereas a method of the above category, and more specifically the "Ecological Footprint Method" satisfied to a maximum degree the criteria set and was considered therefore as the most appropriate method for assessing the environmental sustainability of a spatial entity with anthropogenic activities.

Further research is necessary in order to indentify methods that are able to assess economic and social sustainability, hence a more holistic inventory of sustainability assessment methods for spatial entities with anthropogenic activities will be developed. The evaluation process followed provides a basis to address the effectiveness of the methods, to develop evaluation criteria, and to select the most suitable method in any case. Future work by the authors will be undertaken to improve the above-mentioned issues.

Results presented in this study can be further utilized to improve current methods and/or develop new ones. The authors are planning to take advantage of these findings and develop an environmental sustainability assessment framework for spatial entities that will be based on the most appropriate method as mentioned, thus the "Ecological Footprint", which will be able to deal with the most shortcomings of the existing methods.

**Author Contributions:** All authors contributed equally to the text. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflict of interest.
