Study on the Layout of 15-Minute Community-Life Circle in Third-Tier Cities Based on POI: Baoding City of Hebei Province

At present, the planning of 15-minute community-life circle is being actively promoted in China. Taking Baoding City as an example, the status quo of service facilities layout was analyzed based on the POI data. Using the spatial accessibility algorithm, the ranges of 15-minute life circle of more than 1000 communities in Baoding were determined. By calculating the up-to-standard rates of public service facilities in each district, it is found that the allocation of medical facilities and commercial facilities in urban community life circle is relatively perfect, but the allocation of public cultural facilities and pension facilities is obviously inadequate. Based on this, optimization suggestions on the layout of public service facilities in the 15-minute life circle were put forward from three aspects: facilities sharing, function mixing and population structure and activity characteristics differentiation. It not only provides data and technical support for the planning and construction of community life circle in Baoding city, but also provides referable examples and promotable models for the community planning of third-tier cities.


Introduction
In recent years, the concept of "15-minute life circle" has been widely recognized and promoted in China, and gradually applied to urban planning. In 2016, the The research and planning of life circle began in Japan in the 1960s. In 1969, the Ministry of Construction and the Ministry of Land Affairs of Japan put forward the concepts of "local life circle" and "settled circle". Settlement circle was dominated by people's demand for activities. According to residents' daily life needs such as employment, schooling, shopping, medical treatment, education and entertainment, area coverage for planning a day's life was defined as a spatial planning unit. Later, this concept was gradually accepted in Asia. South Korea's residential planning was affected by it, and the allocation of community service facilities was organized with the construction of different levels of life circles. In the comprehensive development plan of 1979, Taiwan also adopted the concept of "local life circle" to classify cities and promote balanced regional development [2].
In recent years, the concept of "circle of daily life" corresponding to community level has been gradually attached importance in China. It has been used in the research and planning practice of built environment assessment and public facilities allocation. Xiong Wei et al. [3] took Nanjing as an example to divide the life circle and select public facilities factor such as public service facilities and public space to evaluate the suitability of human settlement environment. Wu Qiuqing [4] discussed the allocation renewal strategy of community service facilities in mega-cities Megacities from the Living Circle Perspective. Zhao Yanyun et al. [5] compared the differences of public service facilities development in different urban areas of Beijing by measuring the configuration of public service facilities within the 15-minute living circle. Taking Beijing as an example, Chai Yanwei et al. [6] discussed the equalization strategy of public services in different strata and regions based on the spatial and temporal behavior of urban residents. Taking Guangzhou as an example, Xiao Jinghao et al. [7]  the main body of China's development and the "short slab" of modern city construction. Therefore, this paper focuses on the allocation of public service facilities in the third-tier urban life circle, and combines with relevant research to explore the optimal strategies for the allocation of public service facilities in the third-tier cities, taking Baoding City, Hebei Province as an example.
At present, there are two main methods to measure life circle: one is based on survey of residents' daily activities. For example, Sun Daosheng et al. [8] have spatially divided the community life circles by collecting GPS activity trajectories of individual residents in 18 communities. Although this method pays attention to the real behavior information of residents, it may be affected by the behavior habits of some residents, which leads to the deviation of the survey results. The second is to use the analysis method of the buffer. For example, Zhao Yanyun et al. [5] take the entrance of the community as the starting point and 1 km as the radius (15 minutes walking distance), the buffer zone is constructed as the scope of community life circle and the spatial distribution of public service facilities in the community is calculated. However, this method does not take into account the real road network situation, so that the results are not accurate enough. In this study, the existing methods are synthetically used for reference, and the GIS software platform is used to construct the traffic network data set to calculate the real walking path of residents. This method breaks through the limitation of buffer calculation with a certain distance, and also makes the results more authentic.

Data Acquisition
The data collected by the research institute mainly include the datasets of administrative regions, POI data of public service facilities, road data at all levels, and related data of residential districts in downtown Baoding. The data types and sources are shown in Table 1.
Among them, the POI of public service facilities (Point of Interest, refers to the point containing the information of the name, category, geographical location of facilities) is crawled on the Amap using Python tool, and the time node is June 2019. Referring to the Standards for Planning and Design of Urban Residential Areas (GB 50180-2018) and the daily needs of community residents, these data can be divided into six categories: convenient commercial facilities, educational facilities, medical facilities, recreational and sports facilities, dining facilities and pension facilities, shown in Table 2. After data acquisition, cleaning (eliminating invalid information such as errors and duplication) and coordinate

1) Kernel Density Analysis
Kernel density analysis is used to calculate the density of elements in their surrounding fields. It can be expressed as    the quality of residents' daily life. Before calculating the up-to-standard rate of facilities, it is necessary to define the standard according to the needs of residents for different facilities. Its definition is as follows: 1) the overall standard: in categories of convenience business, dining, education, medical treatment, sports & recreation and pension, at least one specific facility is needed to meet the standard. 2) Sub-category standard: considering the substitution between facilities (e.g. Chinese restaurant and fast-food restaurant have strong substitutability, while kindergartens, primary schools and high schools are educational facilities for different age groups. There is no substitutability between them, and they need to exist at the same time).

1) Overall Layout of Facilities a) Convenient Commercial Facilities
As can be seen from the kernel density analysis map of convenience commer-

1) Facility Layout Strategy Based on Reachability and Share
According to the up-to-standard rate of facilities, the overall allocation of community cultural facilities, pension facilities and some educational facilities in Baoding downtown area is insufficient. Therefore, it is necessary to improve the distribution of community cultural activities facilities, implement the indicators of pension services, and build educational facilities for all age groups. At the same time, according to the number of up-to-standard facilities in communities, we can accurately locate the missing facilities in each community, and then conduct precise construction.
For the more frequently used facilities, they shall be allocated in areas within 15 minutes of walk, therefore these facilities can be used by more communities and residents, and to a certain extent, form sharing to improve the service of facilities, shown in Figure 12 and functions according to the size of the population, and combine the functions of community recreation, community pension, non-staple food market and other functions to form an intensive and complex layout form for community residents. Therefore, convenient and efficient "one-stop" life services are established to meet the different needs of residents, and high-quality and efficient community spaces are formed.

3) Differential Layout Strategy for Population Structure and Activity
Features Due to the differentiated, aging and highly educated people living in urban area, the lack of different facilities will bring different influences. While improving the facilities in the community life circle, we should also establish standards of public service facilities that suit the features of population structure. For example, the community with a higher population aging rate should be allocated with more pension service facilities. At the same time, the facilities should be rationally allocated according to the population density and residents' activities, the range of life circle can be expanded in the suburbs, where the population density is relatively low.

Conclusion
According to the research result of POI data of community public service facilities, in the 15-minute community life circle of Baoding downtown area, the allocation of convenient commercial facilities, dining facilities and medical facilities is relatively good; the allocation of community cultural facilities, primary and high schools needs to be improved; and the community pension service facilities need to be constructed urgently. In combination with the actual situation,

Foundation Project
China's National Natural Science Foundation Project "Research on Green Productive Renewal Strategy and Method of Existing Urban Residential Areas" (51708395).