Visualization analysis of research progress for walkability

The study of walkability is of great significance to the construction of healthy cities. In this paper, taking 1283 articles of walkability, which were included in Web of Science, as the research object. This paper adopts to analysis the research progress by using the method of scientometrics and knowledge networks analysis. Objectively and systematically analyze the research progress of walkability abroad from the aspects of publication overview, knowledge foundation, research direction and hot spots, etc. It is found that foreign researches on walkability mainly include three core directions: walkability and physical activity, walkability evaluation, walkability and urban design. Among them, walkability and physical activity orientation have been studied from various perspectives, such as various groups, various environmental types, different behavioral patterns and various chronic diseases. With the increasingly prominent urbanization problems and the rapid development of new technologies, multiple data, new methods and interdisciplinary cooperation will actively promote the vigorous development of walking suitability research.


Country of issue analysis
When the countries of publication were analyzed, all research papers on walking suitability came from 65 countries or regions in the world.Figure 2 shows the top 20 countries or regions with a total of 1677 papers, accounting for 87% of the total papers published, mainly in Europe, the Americas, Asia, and Oceania.Among them, the United States is the most active country in the study of walkability, with 542 articles, accounting for 28% of the total number of articles published, which is more than twice the number of articles published in the second place, Australia.In addition, four Asian countries, China, Japan, Korea, and Malaysia, were among the top 20 countries in this field, and China was ranked fourth in the world with 125 articles, accounting for 6.5%  of the total number of articles published.It can be seen that Chinese researchers have contributed significantly to the development of walkability research worldwide.

Keyword frequency analysis
Studying the evolutionary dynamics of keywords can provide a quick understanding of the research trends and hot spots in the field.The study counted the key words in the field of walking suitability research in WOS from 1997 to 2019 and kept the key words with a word frequency greater than 5 per year (Fig. 3), and found that no high-frequency words appeared in the articles published before 2008, and the research content was scattered without obvious research hotspots.From 2008 onward, some key words began to appear consistently and at high frequencies in the research literature on walking suitability, e.g., physical activity has consistently been an important research content in this field since 2008.Since 2010, the number of research perspectives on walkability has been increasing, and research on the relationship between built environment, walking, obesity, elderly, community environment, urban design, and social environment and walkability has become a research hotspot in the field and has received continuous attention from researchers.In addition, the number of research papers in the direction of travel patterns, virtual reality, and big data is also on the upswing.

Analysis of important journals
A total of 2500 articles within the search were published in 402 different publications.Among them, 199 publications have published only 1 paper in the field, and 21 journals have published more than 10 articles in all, and these journals have published a total of 1003 articles, that's more than half of the total number of articles published.This study counted the 10 most active journals among these 21 important journals (Table 1), mainly in the disciplines of public health, transportation, medicine, sports, urban planning, landscape, and sociology 2 .These journals not only have the highest contribution of publications, but also, 7 journals have the top 10 total citations of their articles, which shows that these journals are important journals in the field in terms of publication volume and academic influence.
At the same time, comparing the total number of citations and the average number of citations of each journal, "International Journal of Behavioral Nutrition and Physical Activity" and "American Journal of Preventive Medicine" are the top two journals in terms of total number of citations and average number of citations.Two, the articles in this field of "American Journal of Preventive Medicine" are far more cited than those of other journals in terms of total citations or both.

Knowledge base
The number of articles published in each discipline was analyzed, and the top ten disciplines were mainly concentrated in the fields of public health, environmental science, transportation, and urban planning.Histcite software was used to build a database of hot literature to further analyze the most influential articles in the field of walkability, as shown in Fig. 4. The top 30 database documents with LCS scores were selected, and the 16 classic documents with more than 100 citations were analyzed.Among them, six articles focused on the potential association between built environment and walking type and physical health; four articles explored the intrinsic association between urban form, transportation, and walkability; four articles explored the related content of www.nature.com/scientificreports/walkability evaluation; the remaining two articles studied the relationship between community walkability and social attributes。

Research directions and hot spots
Keywords can express the research theme of the article, which contains the most condensed content information of the article, and network analysis of keywords can clarify the network structure and relationship strength among research directions.The keywords in the literature were extracted and analyzed by bibexcel software, and 2039 keywords without duplication were retained after data cleaning.The keywords with word frequency greater than or equal to 20 in the literature were listed and counted (Table 2), and the popular directions in the field could be found.Subsequently, the keywords with word frequency greater than or equal to 5 were network analyzed to study the intrinsic structure and association among the research directions of walk suitability.The screening results showed that a total of 121 keywords met the conditions, and then, the above keywords were expressed visually using Vosviewer software, as shown in Fig. 5, where the nodes represent keywords, and the larger the nodes indicate the higher frequency of occurrence.The thicker the line, the more frequent the cooccurrence, the higher the correlation between the keywords, and the weaker the connection strength of some keywords, which may become a new research direction in the future.Different colors represent different clusters, as shown in the figure, it can be clearly seen that the research direction of walking suitability can be divided into 6 clusters.Among them, cluster 1 is walking suitability and planning design; cluster 2 is environment type and behavior; cluster 3 is walking suitability evaluation tools; cluster 4 is the effect of physical activity on chronic diseases; cluster 5 is physical activity of different groups; and cluster 6 is walking suitability evaluation index.Some keywords with significant correlations exist in some clusters, so the six clusters are further divided into www.nature.com/scientificreports/three major research directions: walking suitability and physical activity, walking suitability evaluation, and walking suitability and planning design.Finally, each research direction is associated with different regions, and the existing research directions in each region are summarized, as well as further research directions in the future (Tables 3, 4).

Walk suitability and physical activity
The 2010 Toronto Charter for Physical Activity: A Global Call to Action defines the important role of physical activity in this field of study.Physical activity has multiple benefits including promoting well-being, maintaining physical and mental health, and preventing disease.Walking is a highly recommended form of physical activity as a low-impact, age-appropriate and environmentally friendly transportation choice.

Physical activity for different groups
Physical activity is considered to be an important intervention indicator of health level and is significantly correlated with walkability www.nature.com/scientificreports/influence on walking suitability and an important determinant of physical activity and walking to school in children and adolescents, and there is a significant correlation between perceived traffic safety and walking activity, and this association is stronger in girls than in boys 4 .And reducing traffic volume and traffic speed and increasing children's recreational areas have been shown to be important measures to increase walking safety for children and adolescents 5 .In terms of obesity prevention: physical activity can improve children's health including obesity 6 and cardiorespiratory health 7 .Therefore, promoting physical activity in children to prevent obesity has become a public health priority 8 .Active schooling is also an important part of physical activity for children and adolescents, as well as an important means of curbing childhood obesity 9 .Yu C Y et al. found that parental tooness was a major factor in the choice of schooling, and that among the factors influencing parents to allow children and adolescents to walk to school, in addition to the amount of cars, a good environment, and walking distance, different dimensions such as safety, positive peer influence, and age of combined issues are also important influencing factors 10 .Loh et al. found that off-campus MVPA has a significant positive correlation with leisure facilities (within 2 km), walkability (1-2 km), and residential density (1 km) 11 .Ayse Ozbil et al. found that the spatial structure of the street network around the home is a decisive factor affecting children's motivation to go to school 12 .

Type of environment and behavior
Physical activity can be accumulated in a variety of ways, such as sports, recreation, active commuting (e.g., walking or cycling), and in different environments (e.g., schools, streets, parks, neighborhoods, etc.) [13][14][15] .There is consensus in the fields of urban planning, transportation, and public health that the built environment has a significant impact on whether to support residents to walk or ride.Studies have shown that people get most of their physical activity activities around workplaces, in community settings, and in walking behaviors.These built environments can create opportunities for physical activity 16 .Karen et al. studied the association between objective environmental characteristics and self-reported physical activity in 48 communities in New Zealand and showed moderately strong associations between destination accessibility, street connectivity and residential density and physical activity 17 .Robert et al. used a survey of students in Liverpool to examined the association between school travel, body mass index and cardiorespiratory health and found that active school attendance was associated with higher body mass index and lower cardiorespiratory health index, and that this conclusion was Table 3.Current research directions in each region.
North America Asia Europe Others

Walking environment and physical health
Child health and the built environment 26 Neighborhood environment and physical activity 42 Obesity and walking fitness in children 6,7,26 The built environment and hypertension and diabetes 11 Obesity and the environment 8,21,22 Some important indicators affecting walking suitability on walking 28 School style and physical health 18 Environmental factors affecting type 2 diabetes mellitus 24 Workplace environmental characteristics and walking behavior 16 Children's gender and safety perception 4 Community environmental characteristics and physical activity 17 Built environment and activity mode 22 Way to school Walking environment 10 Influencing factors of juvenile walking safety 5 Walking suitability evaluation the relationship between four kinds of walking behavior and land use mix 29 Urban Construction Environment Survey Tool 35 Riding choice and environmental aesthetic factors for the elderly 30 Evaluation of street walkability using a point system 38 Aesthetic rating of walking 31 Using street pictures to assess street greening and behavior 28 Walking fitness Index 39 MAPS Street audit tool 34 Environmental pollution and walking suitability 32 Walk index website 'Walk Score'(Ivan Blečić et al., 2015) 40 Perceived community environment NEWS or News-A series scale 36 Community level aesthetic rating 31 Walkable and urban planning design Root et al., 2017 31 Built environment and walking community 41 Environmental characteristics affecting the riding experience of the elderly 30 Socioeconomic conditions and community walkability 44 Drivers of pedestrian activity 41 Environmental quality and design tools 40 Neighborhood type and walkability 42 Walkability and community crime 45 Community walkability and air pollution 32 also potentially influenced by community deprivation, commuting distance, and aesthetic street characteristics 18 .Yu et al. found that lower residential density, better aesthetic environment and higher street connectivity will encourage the elderly to participate more in leisure and sports activities.Better access to services will only encourage recreational walking, rather than physical activity, among older adults 19 .Ester Cerin et al. found that complex urban environments and exposure to nature may benefit cognitive health in older adults.For higherorder cognitive abilities, such as memory, these positive effects may be stronger in areas with lower levels of traffic-related air pollution 20 .

Impact of built environment on chronic diseases
Lack of physical activity increases the risk of many chronic diseases, including obesity, hypertension, diabetes, colon cancer, osteoarthritis, osteoporosis, and coronary heart disease.A common consequence of physical inactivity is obesity, which as an epidemic is highly prevalent across all ages, races, and socioeconomic groups 21 .
Obesity is associated with unhealthy lifestyles, education, income, and environmental factors 22 and is associated with a variety of diseases such as cardiovascular disease, type II diabetes, and osteoarthritis 23 .Saelens BE et al.
suggest that the built environment can influence energy balance by providing opportunities for physical activity, and therefore the prevalence of obesity is lower in more walkable communities than in less walkable ones 16 .Tashi et al. used data from more than 200 assessments to systematically analyze environmental factors affecting type II diabetes such as walkability, physical activity resources, food environment, green space, air to pollution, and many other environmental indicators, and the data showed that higher levels of walkability and green space were associated with a lower risk of type II diabetes, while higher levels of nitrogen dioxide, PM2.5, and noise The higher the level of nitrogen dioxide, PM2.5 and noise, the higher the risk of type II diabetes.However, due to limited data, the mechanism of environmental effects on the risk of developing type II diabetes is unclear 24 .Beulens et al., using big data samples from geographically linked electronic health records, analyzed the relationship between land use combination and intersection density in the built environment and hypertension and diabetes, and found that diabetes and hypertension were poorly controlled in African Americans.American patients are less common in more walkable neighborhoods 25 .Jia et al. followed 9440 kindergarten children from 1998 to www.nature.com/scientificreports/2007 and found that in the United States, the better the walkability of the residential area, the lower the children's body mass index and obesity risk 9 years later.This association was found in It's more pronounced among girls and suburban areas 26 .Joline W. J. Beulens et al. believe that air pollution, residential noise, and socioeconomic deprivation at the regional level are associated with increased risk of type 2 diabetes, while neighborhood walkability and green space have been associated with reduced risk of type 2 diabetes 27 (Table 5).

Walking suitability evaluation index
In the process of analyzing walkability, all urban environmental characteristics related to walking may become important indicators for assessing walkability 3 .Existing research results, on indicators of walkability, are divided into two main dimensions: (1) to determine evaluation indicators from urban scale overlooking density, diversity, and design standards to quantitatively describe the overall urban factors affecting walkability.For example, Lu et al., studied the linkage between pedestrian suitability and urban-scale environmental influences in Hong Kong by using population density, land use mix, and street connectivity as evaluation indicators, and found that two indicators, population density and land use mix, were not significantly correlated with any area of walking, while population density was positively correlated with traffic walking and recreational walking only in the lower density range, and in the higher The higher density range was negatively correlated with recreational walking, therefore, there may be no effect on walkability in high-density cities using the above indicators 28 .Lisa et al. surveyed adults in the suburban subway neighborhoods of Vancouver to assess the association between the four walking behaviors of walking to work, walking out, walking for recreation, and physical activity and land use mix and found that living in areas with a high proportion of commercial land, recreational areas with a high Table 5. Finds of several studies on the built environment and health.

Example articles Sample
Data source for environmental factor(s)

Environmental factor(s) examined Walking metric Results
Venurs H. Y. infrastructure, road maintenance, connectivity, and aesthetics that may affect the cycling experience of older adults, and concluded that traffic safety is an important factor influencing older adults' cycling choices 30 .Root E D et al. conducted an empirical study of aesthetic ratings of community walking and used spatial regression models to find that aesthetic ratings were influenced by geography, aesthetic perception, and race 31 .Besides, some relevant factors such as socioeconomic status and air pollution are also important indicators in some walkability studies.For example, Marshall et al. monitored the concentrations of carbon monoxide and ozone in the air in some areas of Vancouver and studied the association between environmental pollution and walkability, and found that areas with low pollution and high walkability are usually located near downtown and are almost always high-income communities 32 .

Walk suitability evaluation tool
The influence of environmental factors on walking has led to a large number of tools to measure environmental walkability.Walkability tools were developed to assess the overall built environment and to help identify and clarify the factors that impede walkability 33 .Currently, research on walkability assessment tools has focused on two components: audit tools and analytical tools.The use of environmental audit tools is mainly to investigate the performance, spatial demand, and walking experience of pedestrian facilities through GIS measurements, questionnaires, and direct observation 34 .For example, the China Urban Built Environment Survey Tool (CUBEST) developed items including six dimensions of residential density, street connectivity, accessibility, sidewalk quality, bicycle lane quality, and environmental aesthetics, and professional investigators rated the environment based on the survey items in the above dimensions 35 ; a series of scales such as NEWS or NEWS-a for perceived community environment research, which has been used by researchers in multiple countries as an audit tool for walkability studies to investigate residents' perceived community environment 36 ; and analytical tools such as scoring systems, simulations, regression analysis, and integral logit models are mainly applied in the evaluation of environmental walkability 37 .For example: Root et al. investigated the factors of community-level aesthetic scores, applied spatial regression models, and the introduced metric of spatial autocorrelation, and verified through empirical analysis that socio-environmental, economic, and spatial structure aspects play an important role in shaping community aesthetics, providing health and planning personnel with ways in which interventions can be taken 31 ; Gallin et al. used a point system to assess the pedestrian suitability of streets, which provides a good basis for evaluating the level of service of pedestrian facilities by rating the surveyed streets with geographic information data and field research assessments 38 .In addition to this, the number of articles on pedestrian suitability evaluation using a composite index is on the rise.The composite index is a summation weighting of the indicators that predict a representative environment that is conducive to walking.As the composite index of walkability has gradually entered more fields such as urban economy, transportation, and real estate, it has transcended disciplinary boundaries to form walkability indices based on different evaluation indicators with specificity.For example, D' Alessandro D et al. proposed the walkability index (T-WSI) measurement method, which uses direct observation of utility, safety, urbanity, and pleasantness, four categories of 12 weighted indicators, to form a comprehensive walkability index and identify streets and elements with low walkability index to support community walkability optimization strategies proposed 39 .With the advancement of geospatial technology and the availability of online maps and datasets, several research teams have developed online assessment tools.For example, the Walk Score, a walkability index website, uses publicly available data (population density, intersection density, block length, etc.) to quickly and freely calculate and score the walkability of an address to nearby amenities, addressing the time-consuming nature of common measurement studies; the Walkshed website has derived a walkability The Walkshed website has spawned a walkability surface tool that assesses the quality and diversity of unimpeded access to an address within a 1-mile radius and calculates a walkability heat map by prioritizing a set of factors by the user; in addition, such walkability tools include "Walkonomics", "WalkYourPlace", and "WalkYourPlace", "WalkYourPlace", etc. 40 .The development of online assessment tools offers a broader prospect for the flourishing of walking suitability-related research.

Pedestrian suitability and planning design
An important purpose of the study of walkability in urban planning is to link it to urban planning and design.
Locations with higher walkability tend to have more active residents and are conducive to a healthy urban life.Walkability is often related to a variety of factors, and the results of this research have contributed to the weighing of pros and cons in the planning and design process, as well as to policy development.
Population density, land use diversity, and street connectivity are considered to be important indicators of walkability.Yi Lu et al. used the above variables to investigate the correlation between pedestrian commuting and recreational walking in Hong Kong and found significantly different results; land use diversity and street connectivity were not significantly correlated with the two types of walking trips, and population density was only positively correlated with pedestrian commuting and recreational walking were positively correlated in the higher density range, and negatively correlated with recreational walking in the higher density range 28 ; Lai et al. explored the drivers of pedestrian activity in cities by integrating multiple datasets on pedestrians and the environment in cities and quantifying place location characteristics.It was found that building density, population density, and public transportation were persistent drivers of pedestrian activity in New York City, while other features of the urban landscape influenced pedestrian activity differently depending on time of day, day of week, and surrounding environment 41 .Zuniga-Teran et al. compared the walkability of four types of communities: traditional, suburban, gated, and clustered communities and found that Traditional communities were the only ones that differed from other types of communities and were friendly to both traffic and recreational walking, but also had the disadvantage of higher crime rates, while enhancing the natural environment and regular maintenance of the community may improve the well-being of residents, regardless of the type of community 42 .As research progresses, some pedestrian suitability evaluation models can be used not only as analytical tools, but also as support systems for planning and design.For example, Ivan Blečić et al. proposed a planning and design software tool, Walk Explorer (WE), which can synthesize the actual routes of community walkability and walking-related environmental qualities, and use a multi-criteria evaluation model as the core of a decision support system to score the walkability of various points in urban space and derive potential walking routes along the street network; it can also be used as a tool to improve the effectiveness, relevance, and inclusiveness of urban design and tool for improving the effectiveness, relevance, and inclusiveness of transportation planning 40 .Jin Rui et al. proposed that measures related to innovative streets can be divided into two broad categories: urban mobility and urban livability.Combining smart street facilities with the Internet of Things (IoT) using grid and radial street networks to create a safe street environment was found to be critical to promoting urban mobility.In contrast, walkable, cycle-friendly and people-centered street environments enhance social interaction and urban livability 43 .
In addition to this, traffic, weather, safety, economic, and psychosocial factors have been shown to be important factors influencing walkability to some extent, affecting the nature and extent of walkability 44 .For example, Sarah Foster et al. studied the correlation between walkability and community crime and found that crime rates were positively associated with walkability and that more walkable neighborhoods also had the potential to attract higher levels of crime, and therefore the impact of crime rates also needed to be weighed in planning and design 45 ; Julian et al. studied the correlation between community walkability and air pollution and found that different urban spatial patterns result in different concentrations of ozone and that low-income areas have both high and low walkability characteristics and higher levels of both motor vehicle tailpipe pollution and ozone pollution.In contrast, high-income areas are generally located near city centers and have low pollution and high walkability characteristics.This shows that the increasing concentration of urban layout and activities can bring both better walkability and air pollution disadvantages, and therefore, more external factors of the built environment need to be incorporated into the planning and design for comprehensive consideration 32 .

Summary and discussion
This paper uses scientometrics as the theoretical basis for data analysis and combines knowledge network analysis methods to conduct knowledge mapping analysis of literature published in the Web of Science database from 1997 to 2019, which visually presents the overall publication situation of the existing literature in walking suitability-related research.With more and more research results confirming that physical health and sustainable development are closely related to the walking environment, the research on walking suitability has received increasing attention and the number of publications has increased significantly.The research content is gradually diversified and refined, incorporating multidisciplinary knowledge from public health, urban planning, transportation, behavioral science, geography, etc., and gradually penetrating into research with different populations, different behaviors, different types of environments, multidimensional indicators, and multiple data.Research methods have also shifted from early research and qualitative analysis to a comprehensive research approach that combines multiple data, constructs assessment models, and combines qualitative and quantitative, static and dynamic.Due to the accelerated urbanization and the increasing health problems, the research directions related to the evaluation of walkability, walkability and physical activity, and walkability and planning and design will continue to be the focus of attention in the future.In terms of walking environment and physical activity, researchers mainly focus on several key directions, including: different groups and physical activities, environmental types and behavioral patterns, and the impact of the built environment on chronic diseases.Research results in various regions mainly focus on the impact of the built environment on walking activities and travel patterns of various people.North America and Europe have also conducted a large number of studies on the impact of the built environment on various chronic diseases such as obesity and diabetes.In future research, various.The region will continue to pay attention to the impact of the built environment on chronic diseases and infectious diseases, and the impact of the built environment on children and the elderly.Researchers in North America will also focus on how to use different types of data and different research methods to improve the quality and accuracy of research.Sexually speaking; Asia is affected by dense population and development stage.The built environment and mental health, green exposure and physical activity, and pedestrian environment design in the urban renewal process will also be key areas of future research.In terms of walking suitability evaluation, walking suitability evaluation indicators and walking suitability evaluation tools are two important research directions.Currently, various regions are focusing their research on developing various street audit tools to formulate a system for different groups of people, different environments, and Various evaluation indicators are used in different ways, and many researchers have developed different evaluation tools for walkability; North America will explore the inclusion of more methods and more interdisciplinary research into research in this field, and explore more accurate indicator threshold; Asia will continue to focus on research on perceived environment and objective environment, street view maps and machine learning; Europe will conduct in-depth research on urban quality evaluation and spatial simulation using multi-source big data.In terms of walkability and urban design, it mainly discusses how to apply the research results in this field to the urban design process.The impact of air quality, climate and other aspects on the built-up area and pedestrian environment is a continuing concern of researchers around the world.Research directions, in addition to smart cities, micro-communities and how walkability guides urban policies, are also very valuable research directions in this field.www.nature.com/scientificreports/Based on the above research, the following are some suggestions for the future research on walkability in China: (1) Combine the national conditions of China and reasonably draw on the research results from home and abroad.There are many inconsistencies in the results of research on walkability, which may be related to the acquisition of research data, interpretation of analysis results, and cultural differences between cities. (2) Expand the depth and breadth of research.Although the research on walking suitability in China has been carried out late, there have been many promising results, including studies on walking suitability evaluation, street vitality, physical activity, public transportation, etc., which have accumulated valuable information for the development of walking suitability research.However, it is still found that the research results in China lack richness in terms of research content and research methods, with more case studies and fewer empirical studies.Researchers still need to combine the actual situation of urban development and search for research content and perspectives among the relevant theories and achievements in the fields of public health, urban planning and behavioral science to meet the needs of urban development.(3) Strengthen interdisciplinary cooperation and application of new technologies.China's cities face various problems such as traffic congestion, health risks, and air pollution, and research related to walkability needs to seek interdisciplinary complementary advantages and expand new ideas and achievements.Meanwhile, the development of big data, geographic information technology, and artificial intelligence has provided new algorithms and data sources for urban environment measurement, human behavior activity monitoring, and walking suitability definition, creating new perspectives and ways of thinking for researchers, and the application of new technologies for walking suitability research has become the frontier of research in this field and has provided the possibility for its continuous development.

Figure 1 .
Figure 1.Overview of the number of articles published annually.

Figure 2 .
Figure 2. Ranking of the total number of articles issued by the country.

Table 1 .
Top 10 journals by volume of published articles.

Table 2 .
3. Since 2005, a large number of studies have been conducted on the physical activity patterns and environments of different populations, mainly involving children, adolescents, adults, older adults, women, and low-income groups.In children and adolescents, for example, research on physical activity and walking suitability has focused on safe walking, obesity, and school attendance.Traffic safety is an important Walkability keyword statistics.

Figure 5 .
Keywords network analysis.

Table 4 .
Future research directions in each region.