Research on accessibility and calculation of accessibility on a national scale

 

 

 

I have been thinking about how to calculate the accessibility of the national scale recently.

 

Accessibility, usually defined as the degree of accessibility that a place can reach from another place. Some are also called accessibility and accessibility. However, it is clear that the concept of accessibility is more appropriate to study the concept of accessibility within a city on a regional scale or even a national scale.

 

The accessible degree calculation methods mainly include: distance method, utility method, topology measurement method, gravity measurement method, contour method, cumulative opportunity method, equilibrium coefficient method, and time-space method, it can be divided into three categories:
1) transportation facilities Method Based on the transportation system, common indicators are spatial straight line distance, actual distance, average travel time consumption, average travel speed, travel distance per unit time, bus line density, and blocked degree of road network; 2) activity method based on land use system, such as distance method, contour method, gravity model method, Balance Coefficient Method, and time-space method; 3) utility method based on individual income. Almost all of these methods are extensions of the distance method or are based on the distance method.

 

Generally, the study of accessibility includes two scales: internal and macro regional scales, one is internal traffic and the other is external traffic. In the internal scale of the city, accessibility is widely used as an indicator for the Efficiency Evaluation of the urban traffic system, to a certain extent, it reflects the connection between a city's structure, land use, planning, and infrastructure. On a macro-regional scale, spatial-distance-Accessibility has become a prerequisite for the integration and development of urban areas. The accessibility of traffic networks directly affects the evolution and development of regional patterns.

 

1. accessibility within the city

 

There are several situations to study the internal accessibility of a city. First, the overall urban traffic accessibility can be understood as the traffic location, with many models and methods, for example, considering road density, time distance or cost distance of important nodes such as distance centers, transportation needs (population and land, such as employment and residential population distribution, industrial areas, etc.), etc, the expressions can be divided into consecutive raster maps unrelated to administrative units and raster maps based on administrative units or plots. The second is the accessibility of important public facilities, lawns, and commercial centers, for example, the analysis of green accessibility in Beijing is to analyze the transportation distance and transportation time of each region to reach each green space, and summarize and express the distance according to each green space or each land block to obtain the accessibility of green space. For the internal accessibility of the city, the requirements for data and models are relatively high, and network analysis and shortest path are used for distance calculation. The required data is informative.

 

There is also a kind of analysis called commuting circle, that is, taking a node or a city as the center and calculating the distance range that can be reached at different times. For example, one-hour or three-hour in Beijing.

 

2. Regional macro-scale accessibility

This is my current research. The method and model of the Study on the accessibility of regional macro-scale are relatively vague. Most of the factors such as the regional spatial structure, transportation infrastructure, road density and distance are considered. In my opinion, there are three factors that affect accessibility:

First, we need to consider the location of the region in the whole region and even the whole country's natural and economic geography. This includes some innate factors, such as even if there is no transportation facility, beijing and Nanjing are also more accessible than Lhasa and Heihe. The indicator of this factor is: the effective distance from the region to the Central City, and the total distance from major cities in China or the average shortest distance, the so-called limited distance is the road distance rather than the straight line distance.

Second, considering the degree of development of transportation facilities, the road density is mainly measured by road density. The road density includes the road density of roads, railways, and water transport channels. The larger the road density, the better the accessibility, compared with the third point, this also considers such a situation. For example, when there was only one road between the two cities and then there were several more repairs, if we only considered the first and third points, the accessibility does not change, so we need to consider road density.

Third, when the research scale is relatively meticulous, we need to consider the convenience of transportation, that is, the distance between the region and the transportation trunk lines, ports, and airports, the closer the transportation facilities, and the better the accessibility. There is almost no such factor in the study of provincial accessibility, but it should be considered if it is at the county level or even township level.

 

There are two ways to calculate the accessibility of macro scale:

First, attribute calculation is performed based on the Administrative Unit, and the accessibility of each administrative unit is calculated. The results are expressed in the Administrative Unit space, for example, the distribution of the accessibility of prefecture-level cities nationwide. That is, the distance between each administrative unit and the central city or all major cities in the country, the road density, and the nearest transportation facilities are calculated. Weights must be taken into account for the calculation of these three indicators. The distance from the main city can be based on the GDP and population of the city, that is, the closer the city to be calculated, the greater the GDP and total population of the city (that is, the possibility, significance, and total amount of the city), the better the accessibility; the weight of the road density is determined by the road level or average speed of the road. For example, the distance between a high-speed railway and a highway is greater than that of a national highway or a provincial highway, and the distance from the nearest transportation facility is also the weight of the Transportation facility level.

 

The second is to ignore administrative divisions and perform continuous accessible Computing Based on road networks and important city nodes as the basic data. Calculate the accessibility of each grid. Considering the distance and road density from the grid to all cities (GIS line density calculation, in the first method, road density includes property calculation, not space calculation) distance from the grid to the transportation facilities (the distance between the road network is reduced using GIS ). The weights should also be taken into account for these three indicators. The distance from the main city can be based on the GDP and population of the city. The road density weights are allocated based on the road level or average speed of the road; the distance from the nearest traffic facility is also based on the transport facility level as the weight when the distance attenuation.

It should be noted that there are repeated calculation components in this method. The last two kinds of road density and road Distance Attenuation Process have similar geographical connotations, generally based on different calculation radius, the distance between a grid and a city is naturally high. When calculating the distance from a grid to a city, the path calculation in network analysis should be used, that is, the road distance, this also includes the distance from the road facilities. If the weight of the path is considered, it is also the same as the weight of the subsequent traffic facilities.

 

These two methods are required to calculate the accessibility of the national scale. The first method is used for the indicator comparison at the administrative unit level and subsequent policy analysis, it can be linked to socio-economic indicators for correlation regression analysis and in-depth research. The second method can be used as the basic data of accessibility, you can directly analyze multiple levels of units at the provincial and municipal levels, and perform more in-depth spatial analysis. That is to say, there are two maps of the National Traffic accessibility.

 

In addition, it can also display the internal traffic accessibility of a city in a macro scale, that is, the internal traffic accessibility of each city as a value, we can use indicators such as the internal road traffic density (available in the urban statistical yearbook) and the number of buses to measure the traffic accessibility of all cities in China.