GIS - based Road Network Analysis and Bus Route Evaluation in Futian District, Shenzhen

— Futian District is the central urban area of Shenzhen and one of the busiest and most dynamic urban areas. This article is based on the spatial analysis method (slop, density, road area); Simultaneously, using research methods such as average station distance, nonlinear coefficient, service area

In the process of urbanization, the diversity of production conditions in cities has promoted economic development. "Urban image" is its soul, and the transportation road network is its blood delivery artery, closely related to social pulsation, life dynamics, and economic development. Therefore, transportation is the fundamental, leading, strategic, and important service industry of the national economy and the urban foundation of public construction. It is an element that is related to the national economy and people's livelihoods (Wang, 2017  Based on the above viewpoints, it is important and necessary to analyze the road network and evaluate bus routes in Futian District (Yin & Yu, 2020

Data Sources
This article mainly uses three types of data: one is the vector boundary range data of Futian District, the other is DEM elevation data, and the third is road network data. The road network data includes bus stop and route data ( Table   1).

III. METHODOLOGY
This study uses vector, DEM, and road network data as the analysis materials and is based on spatial analysis methods (slope, density, and road area).
Meanwhile, using research methods such as average station distance, nonlinear coefficient, service area, and bus network repetitive coefficient, combined with national standards, the urban road network and bus network of Futian District, Shenzhen, were analyzed and evaluated ( Figure 2).

Density Calculation
Road network density, reflecting the activity level of regional economic activities and other factors, is an important indicator for measuring regional development (Kong & Zheng, 2021

Slope Calculation
Slope refers to the ratio of the height difference between two points on the same slope section of a route to their horizontal distance. The meaning of its measurement is that the road slope represents the quality index of the city's construction level, the government's behavior, and its vision. The percentage method is the most commonly used method for measuring slope, which is the percentage of the elevation difference between two points to their horizontal distance. The calculation formula is as follows (Yan, 2021): The idea of calculating slope in GIS ( Figure 3) is to obtain the elevation difference of the road, divide it by the length of the road, and calculate the slope of each section of the entire road to obtain the slope value of a road. Main approach: (1) Using the "Mask Extraction" tool, DEM grid data is extracted from road vector lines, and corresponding grid pixels within the defined area of the mask are extracted to obtain DEM values along the road.
(2) Extract the highest and lowest elevations along the road and calculate the elevation difference of the road by interpolating the two.
(3) Using ArcGIS's attribute table tool to calculate geometry to obtain the length of the road.

Road Area Calculation
The urban road area ratio, also known as the  Table 2).

Calculation of Average Station Distance
The average distance between bus stops is the average value of the distance between bus stops and the nearest bus stop. Using QGIS software, the main method is: (1) Select the vector data of the bus stop in the "Input Point Layer" and "Input Target Point Layer", and select the name of the bus stop in both "Fields".
(2) The default output matrix type selection is a linear distance matrix.
(3) Since only the closest site is considered, fill in '1'.
The concept is that it is possible to choose to calculate the distance (0) to all points in the target layer or limit it to the feature that is closest to a number (k).
(4) The final output data points contain vector layers for the distance calculation of each input feature.
Its characteristics and attribute table depend on the selected output matrix type.

Nonlinear Coefficient Calculation
The ratio of the length of a bus route to the straight-line distance between the starting and ending stations is called the nonlinear coefficient of the route.
The nonlinear coefficient of a circular route is measured between the main hub points (or the farthest two nodes) on the route. The nonlinear coefficient can more reasonably reflect the degree to which the bus route deviates from the shortest path of the road network and the detour situation of the bus route. The calculation formula is as follows:

Nonlinear coefficient=length of the line/linear distance between the starting and ending points of the line (3)
This study directly obtains the length of bus routes through the length field of the bus route layer, and the key to calculation is to calculate the spatial straight distance between the initial and final stations of the route.

Repetitive Coefficient Calculation
By using the length field of the bus route layer and road route layer, the length of the bus route and road  in the process of generating service areas, the analysis results will simply outline the surface contour based on the nodes, which contain un-generated routing segments.

Evaluation Criterion
This article mainly uses the "Code for Urban Road Traffic Planning and Design GB 50220-95" as the evaluation standard and adopts the relevant provisions on urban public transportation and urban road systems.

Regulations on Urban Public Transportation
The density of the public transportation network planned in the city center should reach 3-4 km/km 2 , and in the urban fringe areas, it should reach 2-2.5 km/km 2.
As a transportation method with high capacity, energy conservation, environmental protection, safety, and convenience, the importance of public transportation has gradually been recognized by people.

Regulations for Urban road Systems
The urban road land area should account for 8% to 15% of the urban construction land area, and for large cities with a planned population of over 2 million, it should be 15% to 20%. The planning indicators for various types of roads in large and medium-sized cities should comply with the provisions of Table 3.

Traffic Network Density
According to the density map of the transportation network in Futian District, the overall difference in road network density is significant, with a high density in the southeast and a low density in the northwest. The      (Table 4). The national standard requires a density of 3-4 km/km 2 for branch roads, and the density of branch roads in Futian District is about 3.87 km/km 2 , which is greater than 3 but less than 4. It also meets the national standard requirements, but there is no excess.

Road Area
According to the analysis of road area data from level 1 to level 4 (Table 5)  According to the comparison of the analyzed data, it can be seen that the width of the expressway is 35m<40m, which is 5m less than the minimum value of Moreover, insufficient road space may make the driving experience uncomfortable. Vehicles driving on narrow roads may be restricted and unable to maintain a stable speed and direction.
In addition, when the road area is insufficient, the distance between vehicles and other vehicles or obstacles will decrease, bringing unnecessary pressure and tension to the driver. Therefore, in order to ensure traffic safety and smoothness, the road area in Futian District, Shenzhen, should be reasonably planned and designed according to national standards and actual traffic needs.

Road Slope
In terms of road slope analysis, seven long and representative roads were selected as the main ones, km/h, so the maximum longitudinal slope is 5%. The maximum speed required for the main road is 60 km/h, so the maximum longitudinal slope is 6%. The analysis of data related to the seven main roads (Table 6, Figure 6) shows that the slopes of all seven main roads meet the requirements.

Fig.6 Slope of Seven Main Road
Divide the highest and lowest elevations of the seven main road-related data points by 100 meters and calculate the average data. Compared with the 1000-meter division method, the data is more accurate, and calculating the longitudinal ratio of the road will be more in line with the expected value. Taking Shennan Avenue as an example, the slope value calculated through the main road slope formula is 0.398%, which is in line with the expected value, while Xiangmihu Road has the largest difference in slope, which is 1.75%.
However, no matter which road it is, its longitudinal slope ratio is far lower than the national standard. If the slope is too small, it will increase the burden of road maintenance because it is not conducive to drainage and is prone to water retention. Over time, it will lead to road deformation and sand formation, affecting the service life of the road.
Therefore, the slope construction of roads in Futian   (Table 7), which meets the national requirements for the density of public transportation networks in the main urban area.
According to the analysis of spatial distribution, it is also shown that the bus stops are relatively dense (Figure 7).

Lines
Data shows that the nonlinear coefficient of public transportation routes in Futian District is 1.45, slightly greater than 1.4 (Table 9). Overall, the impact is not significant, but for residents in some areas, it will increase time and travel costs, as well as government and public funding and infrastructure construction costs.
It is recommended to further adjust the public transportation routes in Futian District, reduce the nonlinear coefficient, and align with national standards.  (Table 10).
The bus service area within 500m is far below the national standard, and it is necessary to vigorously strengthen the service scope of bus stops.

Nearest Stop for Public Transportation
Calculate the average distance between the bus stop and its nearest bus stop (Table 11). The data shows that the average distance of the distribution of stations in Futian District is less than 500m, mostly within a reasonable range. Among the surveyed stations, only the distance from the exhibition center south to Dongfang Yayuan is more than 500m, which is basically in line with the national standard GB50220-1995.
However, it is still recommended to adjust the distribution of some stations, improve the distribution network of public transportation stations, and make it more reasonable. District, Shenzhen, is significant, with a high density in the southeast and a low density in the northwest. The traffic network is mainly distributed in the east, south, and west regions. Except for the branch roads (fourth level roads) that meet the national standard, the remaining first, second and third level roads in the urban road area do not meet the requirements of the national standard, and some even seriously do not meet the requirements and should be taken seriously and improved. In terms of the slope of the main roads, the seven representative roads selected all meet the requirements.
The public transportation network density of public transportation is 3.056km 2 , which meets the national requirements for the density of public transportation networks in main urban areas. The repetitive coefficient of public transportation lines is 7.74, which is greater than the standard of 1.25-2.5 for the network repetition coefficient specified in the Transportation Engineering Manual. The nonlinear coefficient is 1.45, slightly greater than 1.4. The nonlinear coefficient of bus routes is too high, which can lead to a long detour distance and increase the travel time cost of passengers, which is not conducive to attracting bus passenger flow. In the long run, the increase in transportation costs will be detrimental to the cost-effectiveness of urban travel. In addition, the bus service area within 500m of Futian District is far below the national standard, and it is necessary to vigorously strengthen the service scope of bus stops.
Overall, based on the evaluation of the road network and bus routes in Futian District, Shenzhen, this article found that the planning of the district has shortcomings, mainly manifested in the fact that the urban road area does not meet national standards, the nonlinear coefficient of bus routes is too high, and the bus service area within 500m is far below national standards. If Futian District wants to further develop its city, it should face up to the shortcomings in road design and public transportation layout, explore its own advantages, and adjust its planning strategy to seek new directions and strategies. However, taking the shortage of urban land resources in Futian District as an example, the road network construction in the future of the city may need to develop in a three-dimensional direction, but this is not conducive to the landscape shaping of the city. Therefore, it is necessary to plan the corresponding measures as soon as possible.