From accessibility of traffic to accessibility of service: the spatial analysis of N-minute service circle of urban park system

ABSTRACT As an important strategy of basic public services in China, service “accessibility” follows the concept of fair and equal public services. Compared with the traditional transportation accessibility, it is also a comprehensive consideration from the dimension of residents’ demand and service supply to promote the balance of urban park space layout and service coverage. Based on the N-minute service circle, this study establishes a comprehensive evaluation index system to quantitatively assess the service balance of urban parks based on three dimensions of service availability, spatial balance and social equity, taking the Shangcheng District of Hangzhou as an example. And further, an optimization model of urban park system is constructed to carry out spatial analysis and optimal adaptation of urban park system by combining residents’ demand and evaluation. The results show that the overall accessibility of urban park services shows a spatial pattern of “high in the north and low in the middle”, with obvious spatial differentiation along the river area. The urban park system optimized by the model based on the assessment results achieves the “accessibility” and “refined” quality of urban park services. Meanwhile, this study provides a reference for building a more all-age and quality urban park system. GRAPHICAL ABSTRACT


Introduction
As an important part of public service facilities, urban parks play an important role in the human settlement environment and are the link between various functional areas in urban and community spaces.In addition to the functional characteristics of landscape viewing, leisure, recreation and ecological conservation, they are also social and integrated.However, the difference between the planning and construction of the urban park system and the service quality makes the community residents have a great imbalance in the enjoyment and sense of use of urban park services.In addition, the strategy of China's basic public service system focuses on the "equalization" of public services, and the "accessibility" and "fairness" of public services are important manifestations of equalization.The concept of accessibility refers to whether the distance, time, content and other factors of public services are convenient for users to enjoy the services (Andersen 1972;Shengelia 2005& Zheng 2020).It is not only an important factor to measure the implementation of basic public services, but also an extension of the concept of fairness.The premise to achieve fairness is to ensure the accessibility of service facilities.Service accessibility has a deep research foundation in terms of the geographical space accessibility of public facilities, service availability, accessibility, service quality and comprehensive perspective, which has important theoretical value and research significance for the study of the service balance of urban parks.
The concept of park city is based on an important supplement to the theory and practice of life circle planning.It focuses on the bottom line guarantee of basic living facilities in communities, and reflects the important humanistic care of Chinese style community modernization in the new era.The public green space and urban park system adjacent to the community are important.As a three-dimensional space for human activities, urban parks can create living spaces that meet psychological and emotional needs, and create new lifestyles and space scenes.Many scholars have studied the suitability of urban park services and community residents' needs (Hu et al. 2022), the correlation between urban park spatial layout and population distribution (Li 2013), the quantitative evaluation of urban park services (Wang and Chen 2022), and the spatial layout planning of urban park green space (Tao et al. 2019;Wang et al. 2022& Xu 2021).With the wide application of new technologies, many scholars have tried to introduce models to explore the spatial planning layout (Li, Zhai, and Chen 2021), social equity (Liu et al. 2022) and service quality of urban parks (Yao and Chen 2022).
At present, due to the abundance of space activities and the improvement of the quality requirements of human settlements, the planning and construction of China's urban park system pays more attention to the matching degree with residents' need (Liu et al. 2022) and the balance degree of service enjoyment.However, due to the differences in the space planning and service quality of urban parks, the spatial distribution of urban parks in local areas of the city is unreasonable, the supply and demand situation is not matched, and the quality needs to be improved urgently.Therefore, based on the concept of community life circle (10 min, 15 min and 25 min), this study forms an N-minute service circle that gives consideration to community services, residents' well-being and health vitality, and realizes the fairness and accessibility of the supply and demand of urban park system services in time, space and psychology.And take the urban park system in Shangcheng District of Hangzhou as the research object, discuss the balance degree of the accessibility of urban park services, so as to build a full age urban park system that meets the needs of residents and can provide accessible services.

Overview of the study area
Shangcheng District, located in the core area of Hangzhou downtown (Figure 1).The spatial layout of some old urban areas is chaotic, and the living ecological environment is poor, leading to problems in the spatial distribution of public facilities.Moreover, due to the steady growth of annual green expansion, there is still a gap in the scale and quality of urban parks, especially the lack of large greenways and green centers.At present, Hangzhou is actively building a "unique international and modern model urban area of common prosperity", striving to optimize the spatial layout, provide better public services, and strive to meet the diversified needs of residents throughout the life cycle, so that the urban green coverage rate reaches 90%.Moreover, after the epidemic, residents have a high demand for the total demand and service quality of urban parks, so it is urgent to explore systematic and ecological renewal strategies.The urban parks in this study are free parks that can serve a certain area, have the ability of recreation and can be used by residents within a certain range.The object of this study is 145 free and open urban parks in Shangcheng District.It can be divided into 10 comprehensive parks, 51 community parks and 84 amusement parks, with a total area of 324.14 ha (Figure 2).The service scope of the urban park is mainly concentrated in the southwest of the study area, and there are large service gaps in Jianqiao Street, Pengbu Street and Jiubao Street (Figure 3).

Acquisition and processing of multi-source data
Land use status data is obtained from Zhejiang Data Open Platform (http://data.zjzwfw.gov.cn/Open data platform provided by Zhejiang government departments), and remote sensing images are obtained through Google Maps for comparison.The vector data of residential quarters will be obtained through the AutoNavi API interface in 2021, and the corresponding attributes will be crawled from Anjuke Weibo in March 2022, including the total number of households, parking spaces, total building area and green space rate.The remote sensing images are used to compare and cover the urban parks, and the locations of each entrance and exit of the urban parks are determined to simulate residents' travel.In addition, we also used python to obtain the scores and number of urban parks in AutoNavi API, Baidu Map and Popular Comments APP.OSM is an open source geographic data platform with great openness and timeliness (Wang et al. 2019;Li et al. 2021).This study involves vector data of urban trunk roads, secondary trunk roads, branch roads and urban expressways.POI data of transportation facilities such as bus stops, subway entrances and parking lots in April 2022 were also crawled through the AutoNavi API interface.
The total population data of the streets are obtained from the seventh population census data and the  statistical yearbook of Shangcheng District/ Jianggan District from 2017 to 2021, but cannot reflect the population of each residential district.Assuming that the population in each residential area can be evenly distributed, the AOI of the residential area is assigned by the population of the administrative street, and the population of each residential area is obtained by taking "the building area of the residential area/the total building area of the residential area in the administrative street" as the weighted field (Niu and Tang 2021;Lu and Fang 2019).In addition, the number of households in each residential district was checked by "the number of households in the residential area (obtained from Anjuke) * 2.37 (the average household population in Shangcheng District is 2.37)", which confirmed the accuracy and scientificity of the population data.The gap between the check results was 5.6%.As dynamic source data, Baidu Thermograph can dynamically display the degree of population aggregation.The darker the color is, the more crowded the population is (Qiu, Yu, and Ma 2022;Wang 2018).On May, 2022, this study took two hours as the time node to obtain the Baidu thermal map from 11:00 to 21:00.According to the extraction method of population activity quantity proposed by Zhang Hailin, a unitary linear relationship reclassification function between population aggregation density and alpha value was established to extract the population activity quantity (Zhang 2021).
Import the above-mentioned basic data into the ArcGIS platform, and establish the corresponding spatial database, which is convenient for data analysis using ArcGIS in the later stage (Figure 4).

Selection of evaluation indicators
The supply level of urban parks can reflect the quality and enjoyment of services provided by urban parks to community residents.The degree of community residents' demand for urban parks will also reflect the intensity of residents' demand for urban parks, representing residents' social and spiritual needs for urban parks.The temporal and spatial connection between the urban park and the community (actual traffic starting and ending points, road construction, traffic convenience, coverage of traffic facilities, etc.) can directly affect residents' willingness to go to the urban park.Therefore, this study analyzes the influencing factors of the spatial layout of urban parks from three aspects: supply factors, connection factors, and demand factors.And it builds a comprehensive evaluation system for the accessibility of urban park services based on the classification criteria of the "five-dimensional measurement method" of accessibility.Based on the field survey results of urban park service accessibility (Feng and Li 2020;Han and Zheng 2021), it is divided into 4 first-class indicators and 15 second-class indicators.In the first level indicators, geographic accessibility represents the spatial distance and convenience between residents and urban parks, service availability represents the matching degree between urban park supply and residents' demand, service balance represents the fairness and balance of urban park services, and quality acceptability represents the residents' acceptance and recognition of park services.Indicator attributes and reference meanings are shown in Table 1.

Determination of evaluation index weights
Analytic hierarchy process is a comprehensive decomposition, judgment and result evaluation method, which is highly subjective, while the entropy method belongs to the objective weighting method.The weight is determined by the index entropy value, and the result is more objective.The combination of subjective and objective can make up for each other's defects, so the comprehensive evaluation index γ ij of service accessibility is obtained by combining the evaluation index α ij of AHP and the evaluation index w ij of entropy method.

Basic principles for location selection of urban parks
The location-allocation model is widely used in spatial resource allocation and spatial distribution, and is an important tool to solve facility equity and resource allocation balance (Xu et al. 2022;Gao et al. 2021).The layout of different facilities needs to select models based on their needs and objectives.Therefore, this study selects the minimum impedance model, the maximum coverage model and the minimum facility point model to ensure that the cost of urban parks is minimized and the service efficiency is maximized.The calculation principle and the corresponding equation are as follows.
The decision variables Z i and X i are given by: In formula (1), take 1 represents in i is covered by the selected facility points, take 0 represents i is not covered by the selected facility points; I denotes the set of demand points, i denotes a particular demand point.
In formula (2), take 1 represents in j is selected as a facility points, take 0 represents j is not selected as a facility points; J denotes the set of demand points, j denotes a particular demand point.
(1) The minimum facility point model The minimum facility point model is to select the best facility space location from the given facility points, so that the demand points within the given range are the most and the facility points are the least, the objective function MinX is given by: Each demand point within the set impedance time horizon can be covered by a facility point with the constraints of Formula ( 4)-( 5): (2) The maximum coverage model The maximum coverage model is used to select the most appropriate location under the limit of the number of defined facility points, so as to maximize the demand points within the maximum service radius of facilities within a given range, the objective function MaxY with the goal of ensuring that the allocation of urban park resources achieves maximum equity is formulated as: The constraint formula to ensure that urban parks cover the demand points is: The formula for expressing the number of selected urban parks is: In formula ( 6)-( 8), P is the number of selected urban parks, Zj; Xj 2 f0; 1g; i ¼ 1; 2; � � � ; m; j ¼ 1: (3) The minimum impedance model The minimum impedance model is to select the most appropriate location among all candidate points according to the determined number under the restriction of the number of established facility points, so as to minimize the sum of travel costs of the nearest facility point.The minimum distance from the facility point to the demand point is D. The equation of its objective function MinZ is: The formula to ensure that any residential demand point corresponds to a park facility point is: In formula ( 9)-( 10

The principles of park scene shaping
This research takes community residents as the core, and creates new park scenes through "scene force" to achieve multi-dimensional promotion of urban park services.Drawing on the development concept of "Park City" in Chengdu (Shiet al. 2022;Zeng et al. 2020), the basic principles for shaping the urban park scene in the upper urban area are proposed: (1) High-quality living scene: Build a park scene with emotional resonance and diverse integration Focusing on human settlement environment, we will integrate living, work and transportation with the urban green environment, build an open community with space integration and scene penetration in combination with the community life circle, integrate the public service space of the urban park and the diversified life forms of the community into an integrated community circle, and provide a diversified integration scene for residents.
(2) Health-vitality scene: Build a park scene that combines health, vitality and ecology Connect the concept of ecological health with the community life circle, form a space service mechanism with community connotation by building a dynamic, interactive and ecological park scene, improve the vitality allocation of space with residents' sense of identity, satisfaction and aggregation, and guide the formation of a healthy scene space with ecological vitality.
(3) Humanistic-park scene: Build a park scene with distinctive features and culture-led Through the excavation and implantation of cultural elements, symbols and spirits, the unique and differentiated development of space is guided as a whole to form a park space scene with cultural characteristics.In particular, the construction of cultural scenes combined with the urban space mechanism can create a humanistic park scene that suits the residents' life and has a sense of identity.
(4) Landscape-ecological scene: Build a park scene integrating the form of "mountain-waterpark" Landscape natural space can improve and enrich its ecological landscape and regional characteristics in the city, integrate the natural mechanism of open space and landscape, excavate ecological characteristics and improve the quality of space, and build a distinctive "mountain-water-park" scene space.

Building the human-land linkage optimization model
The optimization model of human-land linkage in this study includes two parts: the first is the optimization of the spatial layout of urban parks, the model is used to determine the optimal location quantity and area scale of urban parks, and the service allocation and scope delineation are carried out in combination with residents' needs.The second is the guidance of urban park scene shaping, based on the basic principles of park scene shaping, the park scene is guided by modular design.

Analysis of the accessibility of urban park services
The spatial analysis of various indicators is conducted through ArcGIS, and the comprehensive evaluation results of the accessibility of urban park services are obtained through weighted superposition, which are visualized based on the natural fracture point classification (Jenks).

Evaluation results of geographical accessibility
The comprehensive score of geographic accessibility of each street in the study area is relatively low, with an average value of 0.076, which is below the average value.The overall balance varies greatly.For example, Hubin Street has the highest comprehensive score of geographical accessibility, but the score of the number of urban park gates in this street is relatively low.The comprehensive evaluation of geographic accessibility of Sijiqing Street, Ziyang Street and Jianqiao Street is relatively low, indicating that the urban parks in these streets need to be improved and optimized accordingly.In particular, Sijiqing Street is only 0.038.The secondary index value of this street is low, and the average distance from start to finish is the highest, resulting in a low comprehensive evaluation result.Therefore, it is necessary to plan the spatial distribution relationship between residential quarters and urban parks in this street (Figure 5a).

Evaluation results of service availability
The comprehensive score of service availability of each street in the study area is relatively low, with an average value of 0.141.The balance difference between secondary indicators and evaluation of most streets is relatively balanced.For example, Dinglan Street has the highest comprehensive score of service availability, and the evaluation results of secondary indicators of this street are relatively high.Among them, the comprehensive evaluation of Wangjiang Street, Ziyang Street, Pengbu Street and Jianqiao Street is low, indicating that the supply of urban parks in these four streets is poorly matched with the demand of residents.The evaluation result of Wangjiang Street is only 0.059, especially the index of per capita urban park area is low, which leads to a low comprehensive evaluation.Ziyang Street and Pengbu Street are second, and the secondary indicators of these two streets are both low (Figure 5b).

Evaluation results of service balance
From the overall point of view, the spatial difference is relatively large.The mean value of the comprehensive evaluation results is 0.078, and each street is below the mean value.The comprehensive evaluation results of the service balance of Wangjiang Street, Ziyang Street, Pengbu Street and Jianqiao Street are lower, indicating that the fairness and balance of urban park services in these four streets are poor.The comprehensive score of Wangjiang Street is only 0.005, and the score of the secondary indicators of this street is very low.The parks in this street are concentrated along the river, which cannot meet the needs of internal residential quarters.It is concentrated in the northwest part, but the urban parks are mainly distributed in the middle area of the street, resulting in that the recreational needs of most residents cannot be met (Figure 5c).

Evaluation results of quality acceptability
On the whole, the mean value is 0.049, and the comprehensive score of the quality acceptability of each street is relatively high, indicating that the residents in the study area have a relatively balanced service acceptance and recognition of urban parks.The lower ones are Caihe Street, Zhanongkou Street, Xiaoying Street, etc., indicating that residents in these streets have poor acceptance and recognition of urban park park services, and urban parks need to be improved and optimized accordingly.In particular, the score of Caihe Street is only 0.017, and the evaluation result of the utilization matching index of the urban park of this street is the lowest.Zhanongkou Street is the second, and the evaluation results of the secondary indicators of this street are also lower.Xiaoying Street also has relatively low comprehensive evaluation results due to the low evaluation results of the utilization matching index of urban parks (Figure 5d).

Comprehensive evaluation and analysis of urban park service accessibility
On the whole, the evaluation results of service accessibility of urban parks show a spatial distribution pattern of "high in the south and north, low in the middle".The spatial distribution is relatively dispersed and has a large difference.Moreover, the service level of parks is far from meeting the demand.The overall service accessibility is poor and the spatial differentiation is obvious.Especially, the administrative unit gap in the riverside areas is obvious, which cannot ensure the service balance and spatial fairness of urban parks in the entire study area, as Figure 6 and Table 2.
The administrative units with high comprehensive level are mainly distributed in Hubin Street and Dinglan Street as two cores in space, and the administrative units close to natural scenic spots have high level, such as Dinglan Street, Hubin Street, Qingbo Street and Sijiqing Street.In particular, Dinglan Street has the highest comprehensive score.The street is located in the urban development zone, with good service balance and availability.However, attention should be paid to the park quality in the area and the emotional connection between residents and the space.
Xiaoying Street, Kaixuan Street, Jiubao Street and other administrative units are at the middle level of evaluation.For example, the quality acceptance and park satisfaction of Xiaoying Street, Kaixuan Street, Zhalongkou Street and Caihe Street are relatively low, which requires targeted quality improvement of their urban parks, and the service balance level of these four administrative units is also relatively at a stage that can be improved.The four indicators of Jiubao Street are relatively balanced, and the spatial distribution of urban parks and residential areas in this part is also relatively matched, which can increase the allocation of small-scale parks in the planning of community life circle, and improve the uniformity and convenience of park services.
The administrative unit with low comprehensive level is mainly divided into two parts, including  Wangjiang Street, Ziyang Street, Pengbu Street and Jianqiao Street.Among them, the comprehensive level of Wangjiang Street is the worst (0.159), because the urban parks in the street are concentrated along the river, which cannot meet the needs of the internal residential community, resulting in the low scores of the secondary indicators of the street.The second is Ziyang Street, where residential communities are concentrated in the northwest, but urban parks are mainly distributed in the middle of the street, resulting in the inability of most residents to meet their recreational needs.These four administrative units are the areas that need to be considered in the follow-up optimization of the urban park system, especially in terms of the spatial layout and quantity and scale of urban parks.
In addition, in the southwest of the study area, although the service accessibility evaluation is relatively high at present, as the core area of urban development, residents' requirements for high-level and high-quality quality and scale of urban parks in the process of urban park development need to be considered in the future.

Optimization and adjustment of urban park system
Based on the comprehensive evaluation results of service accessibility, we need to optimize and expand the space scale of urban parks, fill in service gaps and blind spots, create a balanced spatial pattern of urban parks, and achieve the goal of 90% service coverage in combination with norms and standards.At the same time, guide the scene design of urban parks to ensure the demand of people throughout the year and promote the organic renewal of urban parks.

Determine model parameters
The service circle of "10-15-25 min" is formed by referring to relevant specifications, standards and indicator requirements and combining with the questionnaire results of field research (Table 3).As residents go to the comprehensive park mainly by private cars and buses, the traffic conditions are good, and as the central city, the radiation range should be wider.As an important open space in the community life circle, the community park can travel by electric bicycle, bicycle and walking, and the traffic is convenient.The amusement park should ensure that the goal of "pushing the door to see the green" is met, and the service standard of the five minutes living circle is achieved.

Total resident demand forecast
The population prediction method is based on the Gray GM (1.1) prediction model, which is a series combination with strong regularity obtained after the accumulation of the original data, and then the predicted value is obtained by adjusting the exponential curve (Cui, Liu, and Zheng 2021).It is widely used in the fields of forecasting population development (Li 2020), social consumption structure, agricultural problems (Yang et al. 2021) and forecasting military problems.This study takes 2030 as the target, and forecasts the period from 2021 to 2030 to adapt to the construction of Hangzhou (Table 4).Based on the above projections, the total population of each street can be predicted, but the population of each residential community needs further prediction measurement.This study assumes that the population of residents can be equally distributed within each residential community, and uses the ratio of street and residential community building area to estimate the population of each residential community.
The house prices of residential communities also affect the spatial distribution of the residential population, so the specific operation of this study is to assign the population data of the administrative street to the residential area AOI data, and use "(residential community floor area/total residential community floor area within the administrative street) * (residential community house price/total house price within the study area)" as the weighted field to obtain the population data of each residential community.The population kernel density analysis is conducted to characterize the spatial distribution of the predicted population, among which the population distribution of Caihe Street and Dinglan Street is relatively dense (Figure 7).According to the calculation of the total predicted population, the three types of parks need to increase in size to meet the needs of residents (Table 5).

Identify candidate sites for urban parks
This study also screened the land suitable for construction as an urban park to ensure greater service value for residents' lives.With reference to remote sensing images and the status quo of land use, 310 candidate sites were selected based on field investigations.

Location and scale configuration of urban parks
As an open space, urban parks can improve residents' enjoyment of basic public services and improve the quality of living space environment.Therefore, urban parks and residential land should be matched as much as possible.In areas where the resource supply gap is small, it can be considered to use reasonable expansion of the park to improve the service capacity.In areas with poor park service accessibility, large gap and concentrated population distribution, additional urban parks will be built to fill the service gap (Figure 8).

The planning and layout of the comprehensive park
The extensive parks in the study area are mainly distributed in the outer ring boundary area, while there is no comprehensive park in the eastern central area, so the needs of the inhabitants cannot be met.There is a large blind area, and a comprehensive park at district level needs to be built.The original indicators in this area have not reached 90% performance coverage, and there are some service blind areas in Wangjiang Street, Ziyang Street, Pengbu Street and Jianqiao Street (Figure 9b).The residential areas are generally outside the scope of the comprehensive park.
The minimum facility point model is used for the preliminary site selection.Among them, the existing 10 comprehensive parks are defined as mandatory points.Figure 9a shows that at least 18 comprehensive parks are required for simulation.However, if there are too many parks, service sectors will overlap, which will not promote the efficiency and balance of land use.Therefore, on this basis, the maximum coverage model is used to simulate the newly added comprehensive parks from 11 to 18 in order to select the optimal location and quantity.The results in Table 6 show that the performance coverage rate of the four indices exceeds 90% when 13 size parks are defined, which can ensure that residents of the community in the area can enter the comprehensive park to the maximum and fully meet actual needs.If larger parks are established on this basis, their services will be too saturated, and the service efficiency of urban parks will also be reduced.Therefore, the optimal number of comprehensive parks is 13, and three new ones are needed (Figure 9c).
After choosing the location, it is also necessary to determine the spatial scale of the new overall park according to the simulated overall park location.The service areas of the 13-total parks are delineated according to their respective service and residential areas and then, on the basis of the indicators determined, the ideal service population and parking area of the 13-total parks are calculated (Table 6).The results show that the supply of six comprehensive parks exceeds demand (Figure 9d).Therefore, on this basis, optimizations and adjustments are carried out to achieve balanced service (Figure 9e).The adjustment process is divided into two categories: (1) Balanced distribution of the service population among neighbouring service areas.For example, Service Area 5 is located on the border of Jiubao Street in the study area, but the demand of residents is high.The newly built Comprehensive Park 1 adjoins Fengshou Lake Park, and the excess space of the park is large.Therefore, some people in the east of the service area will be brought to Fengshou Lake Park while the expansion of the park is being considered.
(2) The area and extent of the corresponding comprehensive park in the service area will be increased and some residential areas will be allocated to other service areas.Service Area 2 is located in the Dinglan Street, it is unreasonable to define an area of 32.73 ha as a comprehensive park at regional level.Therefore, if the parking scale is increased, the population in the southwestern corner is assigned to Service Area 3.
After adaptation, the comprehensive park in the service area can meet the needs of residents in a maximum and balanced manner, which not only realizes the spatial balance and efficiency of use of urban parks, but also fully takes into account the needs of residents.

The planning and layout of community parks
The distribution of community parks in the study area is relatively scattered and the northeast part of the study area is smaller.In addition, the size and number of community parks in the western and northern populated areas of the study area cannot meet the needs of residents in predicting population demand.
The coverage of all indicators of the original community park is approximately 70%, indicating that there are many blind areas in the scope of the original community park (Figure 10b).Apart from Dinglan Street, Sijiqing Street, Qingbo Street and Hubin Street, which have a high comprehensive assessment of the service accessibility of urban parks, some residential communities in other street are outside the service area of the community park, and overall service efficiency needs to be improved.The model simulation process of the community park is consistent with that of the comprehensive park, and it should be noted that the model interruption is set to 1200 m.In the process of model simulation of community parks, it is necessary to eliminate the locations that have been selected as comprehensive parks.The model results show that at least 77 community parks need to be set in the study area (Figure 10a).To avoid overlaps of services, the maximization coverage model is used to simulate the number of facilities from 52 to 77.The results show that all indicators exceed 90% performance coverage when defining 62 community parks (Figure 10c).Demand from residents in the Dinglan Street is high, and the size of the community park is large.However, the number and extent of simulated community parks in the Dinglan Street don't meet the basic needs of residents, especially Dinglan Park and Sanyi Park.Therefore, in addition to the park, two suitable candidate places must be added to distract the service population.After the adaptation, there were 64community parks, including 51-original community parks and 13-new (Figure 10d).The verification results also show that adjusting the site selection is appropriate.
The results of the scale assessment show that the supply-demand of the corresponding service sectors of 30-community parks are not balanced, so the adjustment is made (Figure 10e), which is specifically divided into three categories: (1) Increase and adjustment of the area scale of the corresponding community parks in the service area.For example, the service population gap of the Service Area 1 is large, but the park is located on the border of Dinglan Street, the scope of services is limited, and the cost for residents to go to the neighboring park is too high.(2) Operate volume of the adjacent operating areas must be evenly distributed.If the gap in Service Area 5 is large, the residential area on the right side of Qinfeng Street can be assigned to Service Area 4, if the area of Dinglan Park is increased.
(3) The extent of corresponding community parks in the service area will be increased and some residential areas will be allocated to other service areas.For example, Service Areas 27, 28 and 33 are adjacent, and there are some intersections in the distribution of the service area.The population is relatively large, so it is necessary to adjust the size of some parks and the distribution of residential areas.

The planning and layout of the amusement park
It is of practical importance to carry out the large construction of such amusement parks as pocket park, street park and small-micro green areas.The amusement park plays an important role in improving the service of residents.The impedance interruption parameter is set to 500 m in the parking simulation and the existing 84-parks are set as mandatory points.Points selected as comprehensive parks and community parks are excluded from candidate points.At least 150 parks are specified in the preliminary site selection, and 66 new parks must be added (Figure 11b).According to statistics, all indicators of original park are around 60%, and there are large service blind areas (Figure 11a).In addition, the original amusement park has blind areas in all administrative units, and some residential areas are outside the scope of the park's services.Therefore, it is necessary to expand the scope and increase the number of the amusement park.
The site selection optimization of the amusement park differs from the operation of the two types of urban parks mentioned above.The minimum impedance model is used to ensure that residents' travel costs to the nearest park are minimal.The results show that 138 amusement parks indicators exceed 90% of performance coverage (Figure 11c).Therefore, the number of optimal parks is 138 and 63 new parks must be added.The size distribution and area limitation of the park correspond to the operating modes of the two types of urban parks mentioned above.The results of the index calculation show that the supply-demand of the service sectors corresponding to 49-parks are unbalanced (Figure 11d).The adaptation process is also divided into three categories and forms a new parking area demarcation and corresponding service areas (Figure 11e).

Analysis of rationality of urban park layout
In study, the service radius in the network analysis method is measured at 3000, 1200 and 500 m respectively.The rationality of the spatial distribution is checked by the coverage of the municipal park to the residential area, to ensure that the location and spatial distribution of the municipal park can meet the needs of the residents and the actual result.The service coverage of the comprehensive park is 96.34%, and the scattered residential areas in Pengbu Street and Jianqiao Street are not covered.The service coverage of the community park is 94.56%, and some residential areas in Zhanongkou Street, Nanxing Street and Pengbu Street are not covered.The amusement park's scope of services is 92.11%, of which only housing communities in Hubin Street are covered, and some housing communities in other sub-districts are not covered.It turns out that the range of services of residential area and urban park is very well coordinated, the performance efficiency and balance are high and the overall needs of the residents in the study area are met.Although some residential areas are not covered by the scope of one park type, they can be covered by the scope of another park type, and the overall performance coverage rate has reached 98.67%, suggesting that optimized and adapted urban parking space planning can significantly meet residents' recreation needs.However, there are many overlaps in service coverage and these overlapping parts are areas with relatively concentrated populations.Given that the study area is the urban development center, residents have higher demands on urban park demand and spatial diversity, and it makes sense to choose multiple destinations in all overlapping parts (Figure 12).

Final determination of the spatial layout of the urban park system
The spatial layout system of urban parks in the study area is formed by the location selection, scale distribution, optimization and debugging of urban parks and the verification of the results.The number of urban   The optimised room layout system of the park presents a pattern of "three cores, five centers, a belt and five axes", as shown in Figure 14.Overall, the West Lake landscape area, the Gaoting landscape area, the Qiantang River and the canal landscape are infiltrated into each other.The three cores are the green core by the lake, the green core of Qianjiang new town and the green core Jianqiao, which are the key concentration areas of the park green landscape in the research area.Rely on the canal to form the Jianxin canal landscape axis, improve the greening structure from the south of Gaoting mountain to the canal coast, and form a unique mountain water landscape axis.The historic and cultural green landscape axis is formed by shifting to the historical and cultural relics surrounding the West Lake Landscape Area.By combining culture and landscape, culture is permeated into the construction of the park's green landscape, forming a landscape axis with the West Lake culture and Wushan culture

Residents' needs and basic scenes of the park
According to the questionnaire survey, users have a high degree of use in all areas of the urban park, among which the use rate of quiet tourist areas is the highest.The main activities are walking, chatting and sitting idly.In the post epidemic era, the community residents' demand for urban parks, in addition to the functions of ecological leisure and entertainment, also needs to have the functions of health healing and interactive dynamic experience.The park scene shaping provides humanized design according to the residents' activity preference, use tendency, etc., and configures various facilities and scene elements that meet the residents' needs.This study simulates 10  basic scenes of urban parks (Figure 15), and systematically improves the space quality of urban parks by improving and optimizing the basic park scenes.
Like public service facilities, urban parks are an important part of residents' life.It is necessary to consider the mutual cooperation between urban parks and other public service facilities, road traffic network system and landscape greening system.The starting point of the scene shaping in study is people-oriented, complying with people's behavioral needs and use preferences.In addition to the scene shaing of the urban park's own space, it is necessary to organize the community groups within the service scope, ensure the service efficiency, and improve the quality of life through the linkage between the community and the park.

Park scene module design (1) Digital scene of smart park
From the proposal and development of urban wisdom, park city and planning ideas, it can be clearly seen that the current urban development trend has changed from focusing on facility construction and site construction to focusing more on people oriented urban planning and construction, and paying more attention to perceptible, service-oriented and problem solving scenario planning.The digital scene of smart park can enhance residents' perception and improve the space perception dimension of the park by using smart digital technology.The focus of its scene design is how to highlight the core of "people-oriented" through smart technology, and pay attention to the improvement of human services and interaction elements in science popularization, culture and health.Based on the background of digital transformation, Shanghai Institute of Urban Planning and Design has proposed a digital scene framework for smart parks.Its core framework includes four modules, as shown in Figure 16.Under these modules, for different types of urban parks, the framework model of modular management is adopted for elastic configuration. (

2) Ecological scene of cultural park
The natural landscape resources in the study area are superior, and the residential areas and residential groups distributed in the West Lake Natural Scenic Area and Gaoting Mountain Natural Scenic Area are in the natural landscape ecological base.Moreover, Hangzhou has a long history of gardens and Song rhyme, which is unique in Hangzhou.Based on the canal culture, garden culture and Song rhyme culture in the upper urban area, the core framework of cultural park ecological scene is built, which mainly includes three modules, as shown in Figure 17.Under this module, the module scenes are configured according to the different cultural textures and spatial forms of urban parks.

Conclusions
This study takes Shangcheng District of Hangzhou as an example to establish an evaluation index system of service accessibility that conforms to the behavioral and psychological characteristics of residents, and quantitatively analyze the spatial distribution of urban parks and the balance between supply and demand of services.The results show that the overall spatial distribution pattern is "high in the north and south, low in the middle".The spatial distribution is dispersed and has large differences.Except Dinglan Street, Hubin Street and Sijiqing Street, the evaluation results are relatively high, which service accessibility and balance of other streets are poor.According to the evaluation results of service accessibility and future development trends, LA model is used to optimize the location and match the demand of the three types of urban parks in Shangcheng District of Hangzhou according to the preset parameters in order to provide an urban park system that meets the needs of community residents, equalization and organic renewal.The optimized urban parks are in a pattern of "three cores, five centers, one belt and five axes", with service coverage reaching 90%, realizing the balance of supply and demand of resource allocation and maximizing service efficiency.At the same time, based on the four basic principles and ten basic activity scenes, the scene modules of digital scenes of smart parks and ecological scenes of cultural parks are proposed to guide the planning of urban parks to build "scene power", improve the space quality of urban parks, and form an urban park system that conforms to the "10-15-25 min" service circle.Through the research of this paper, it can provide a new path for the research and planning of building an all age and quality urban park system, and can promote the ecological landscape construction in Shangcheng District of Hangzhou, achieve the construction goal of a Park City, and provide high-quality public spaces for residents.

Discussion
This paper evaluates and analyzes the balance and accessibility of urban parks in Shangcheng District of Hangzhou City, and then proposes a targeted optimization and adjustment plan for the urban park system, aiming to better realize the optimization and upgrading of the urban park system, and provide some theoretical and practical guidance for the urban park space planning and scene shaping.In view of the urban development trend and planning principles, the following three suggestions are put forward for the urban park system planning: (1) Improve urban park facilities for specific people and optimize the quality of original urban parks.
Different people have different needs for urban park facilities.At the planning and design level, "peopleoriented" is precisely targeted at different groups, and more high-quality urban parks are provided for specific age groups (the elderly or the young) and specific occupations (educators, business staff or medical staff), such as recreational trails, indoor activity venues, rest pavilion corridors and performance stages, To ensure that different people can enjoy high-quality public space.
(2) Properly build and expand urban parks to promote the flexible development of urban parks.
There is still a big gap in the service blind areas of urban parks, especially at the level of community parks and parks.The service efficiency and service radius of urban parks will be expanded, the barriers of blind areas will be broken, the service pressure of existing urban parks will be eased, and the supply capacity of urban parks in terms of quantity, area, and type will be improved by means of inserting green spaces on both sides of urban roads, street corners and other areas, increasing pocket parks and community parks, and appropriately improving the scale of some completed parks.
(3) Space sharing to ensure the fairness and efficiency of resource allocation.
High quality urban communities and urban parks are not isolated and closed, and urban parks with beautiful environment are not exclusive to highincome people.Neighborhood space and public space of residents of different classes are regarded as a network system, paying attention to the needs of residents of different groups and classes, meeting the needs of various groups in a diversified way, and promoting a diversified network layout.Alleviate the problem of green injustice and class differentiation, and ensure that people can quickly reach the green shared space from the residential area or the work unit.

Figure 2 .
Figure 2. Spatial distribution of urban parks.

Figure 3 .
Figure 3. Spatial distribution of park service areas.

Figure 4 .
Figure 4. Multi-source data geographic information database in the study area.

Figure 5 .
Figure 5. Spatial distribution of evaluation results of primary indicators.

Figure 6 .
Figure 6.Spatial distribution of urban park service accessibility evaluation results.

Figure 7 .
Figure 7. Predicted population distribution nuclear density analysis map.

Figure 9 .
Figure 9. Correlation analysis of comprehensive park optimization.

Figure 10 .
Figure 10.Correlation analysis of community park optimization.

Figure 11 .
Figure 11.Correlation analysis of park tour optimization.

Figure 12 .
Figure 12. Analysis and verification of spatial layout network of urban park system.

Figure 13 .
Figure 13.Optimized and recommended urban park spatial layout system in Shangcheng District.

Figure 14 .
Figure 14.Spatial layout system of urban parks.

Figure 15 .
Figure 15.Schematic diagram of basic scenes of urban parks.

Figure 16 .
Figure 16.Core modules of smart park digital scene.

Figure 17 .
Figure 17.Core module of cultural park ecological scene.

Table 1 .
Comprehensive evaluation index system of urban park service accessibility.

Table 3 .
Determination of final relevant indicators of urban parks.

Table 2 .
Comparison of comprehensive evaluation results of service accessibility of urban parks.

Table 4 .
Population demand forecast in Shangcheng District.

Table 5 .
Statistics of total demand for urban parks in Shangcheng District.
Figure 8. Spatial distribution map of candidate sites.

Table 6 .
Preliminary site selection data of comprehensive park service area.