Introduction

Rural settlements around urban centers (especially megacities) have more changes and transformations in various environmental-ecological, social-cultural, human, economic, physical and institutional-management fields and dimensions (changes in land use, composition and texture of the population, employment structure, rural activity and production system, spatial structure and spatial organization, etc.) compared to other rural settlements, which over time causes the existence of new entities and transformations in many existing identities. In recent decades, the unplanned growth and expansion of such settlements with their specific physical-spatial developments have been a kind of problem or problem that creates the basis for all kinds of crises and facility anomalies, economic damages, environmental pollution, low security pollution, degradation of rural activity foundations, etc. With scientific and documented research and knowledge of the factors of creating such spaces, it is possible to plan in order to overcome risky behaviors and prevent possible damages. From this point of view, the following article, by presenting a comprehensive and integrated approach through meta-analysis quantitative research method and reviewing the research literature in the field of understanding the transformation of rural settlements in metropolitan areas on the one hand, seeks to, by examining the general characteristics of these studies, their nature to It has been analyzed in terms of different dimensions in order to identify the study gaps in this field and realize the necessary platforms to eliminate these gaps and shortcomings in future researches. On the other hand, it tries to answer the following questions by carefully examining the research done:

1. What transformations have rural settlements in metropolitan areas undergone in the space-time process?

2. What are the effective factors in the transformation of rural settlements in metropolitan areas?

3. What are the ways to overcome the challenges of rural settlements in metropolitan areas?

Methodology

The method of this research is based on meta-analysis and a systematic search of sources based on related keywords was carried out in domestic and foreign scientific databases. In order to select suitable and quality scientific researches for meta-analysis, studies were screened and finally 40 documents were selected. Then ATLAS.ti software was used to analyze the collected data based on grounded theory.

Results and discussion

In this section, the research findings are presented in the form of two axes, including the methodological dimension of the studies (type of research, research approach, data collection method) and the content dimension of the studies (research questions, key axes of the studies).

Methodological aspect of the studies: The results of the evaluation of the articles show that mainly the studies conducted in the field of transformation of rural settlements in metropolitan areas, 70% have been done with a quantitative method. 18% of the studies in this field had qualitative methods and only a few studies, 12%, were based on mixed methods. A significant number (93%) have limited themselves to descriptive-analytical titles in their studies, and only a few articles (7%) have been conducted with a comparative analysis approach. Document-library method (45%) and questionnaire (31%) are the main tools in data collection and less than interview tool (24%) are used to collect information.

The content dimension of the studies: in addition to exploring what metamorphoses are, all the studies have also analyzed why these metamorphoses occur. Among the mentioned studies, a small number (9%) were based on the question of how, in addition to what and why, and were limited to providing solutions and suggestions to face the developments of such rural settlements. : Based on the analyzes conducted with the help of content analysis method, a significant part of the studies (49%) have studied the variable of inefficiency of the body tissue in understanding the transformation of rural settlements in metropolitan areas. State-oriented variables and the high level of inter-settlement interactions (17%) have contributed the most to the transformation of rural settlements in metropolitan areas. The development of institutional capacity is a solution proposed by the researchers of previous studies, which was presented in order to overcome the challenges of rural settlements in metropolitan areas.

Conclusion

The results show that most of the researches are descriptive-analytical, which are based on quantitative methods, and less qualitative and mixed methods are used in this type of studies. In this field, qualitative and mixed methods should be increased in the methodological space of studies. The number of studies in the field of rural settlements in metropolitan areas is also associated with a decreasing trend. Perhaps the decreasing trend can be related to the nature of the difficulty of studies in this field. Most of the studies in this field have gone beyond what and considered why; But the reasons and factors governing the metamorphoses have been mainly examined superficially, and there is a need to conduct a deeper investigation of the reasons and analysis of the driving factors. So it is clear that most of the studies in this field have focused on identifying the current situation (identifying factors and processes); Without paying attention to what should be (how). Therefore, in future researches, by strengthening such weaknesses, study questions, especially the "how question", require more attention, which should be selected and investigated with great sensitivity and based on the study gaps in this field.