Study On Spatial Evolution And Street Extension Of Historical And Cultural Towns In Qinling Mountains

Historic and cultural towns,together with historic and cultural cities,villages and traditional villages,are extremely precious historical and cultural heritage in China.Under the impetus of tourism,the contradiction between cultural protection and economic development in Qinling Mountains mountain area have become increasingly prominent with the expansion of the town space and the increasing demand for the improvement of people's living conditions.The 18 historical and cultural towns distributed in four provinces,such as Shanxi,Gansu,Hubei and Henan are selected as the research objects.Through field investigation and testing,it is found that there are widespread problems in the historical and cultural towns of the mountain area,such as the degeneration of the core cultural heritage,the poor physical environment of the street space,the lack of space scale to meet the needs of modern life,and the destruction of the natural ecological environment because the disorderly expansion of the town space.Taking the national historical and cultural town in Fenghuang town of Xian County as a typical sample,the key issues of spatial evolution mechanism,spatial expansion prediction,physical environment improvement of lanes,reasonable scale and extension mode of streets and lanes are studied.Through the investigation and data analysis,the development and evolution of the historical towns in the mountain area can be divided into development,prosperity,depression and revival periods.They are characterized by gradual evolution,discrete evolution,vertical evolution and diversification evolution.Climate in the border area,Valley mountainous area,blocked traffic,migrating population,diversified life,mountain-forest economy and social policy renewal affect the rise and fall of different times.The characteristics of the formation,evolution,spatial growth,historical memory,and adjustment of the growth of the historical and cultural towns in the mountainous area are very similar to the growth and characteristics of the tree rings.They have "the evolution mechanism of similar annual rings",which can be described by the characteristic elements of "core-form-degree",the "core" means cultural remains,"form" means spatial form,and "degree" means spatial measure.It also extracts the development patterns of Qinling Mountains historical and cultural towns with t similar to the circle,the main axis and the multi group.Taking ArcGIS 10.2 as software platform,land suitability evaluation was carried out.Six evaluation indexes,including elevation,slope,river,traffic,built-up area and ancient block,were determined,and the land suitability zoning map of construction land was obtained.Using ArcGIS10.2 and GeoSOS as the software platform,artificial neural network cellular automata(ANN-CA)method is applied to simulate the land use and town space development prediction in different periods.It provides a scientific and reasonable method for the future development of towns,rationally determining the three lines of ecological red line,farmland protection line and the boundary line of urban construction land.By using decision tree generated by decision tree cellular automata(DT-CA),four rules of land conversion in Fenghuang town are extracted,which can directly grasp the spatial evolution rule of a certain historical period.Accurately predict the form and scale of the spatial expansion of the historical and cultural towns in the mountain area,and provide a new method for land space planning.Using Autodesk Simulation CFD method to simulate the wind environment of streets and lanes,taking the ratio of width to height is 0.4~1.5 of historical traditional streets and lanes as the benchmark scale,and by changing the building height and street width under different initial wind speed conditions,it is concluded that the streets can have a comfortable wind environment when the building height on both sides of the street is 9-18 m and the corresponding width is 9-15 m,D/H<1.The sunshine environment of streets and lanes is simulated by using the software of Sunshine Analysis.Taking the accumulated sunshine of 2 hours in cold days as the standard,the width of streets and lanes satisfying the sunshine of buildings on the north side is determined by changing the height of buildings on the South side,and the height of buildings on the south side of streets is H < D/1.40.It is concluded that D/H=0.6~1.0 is the best ratio of width to height for new roadways to meet the comfortable physical environment.Based on the theory of small town science and spatial development,and from the demand analysis of different groups of people,by deconstructing the spatial characteristics of streets and lanes,the elements of "function,structure,scale,node,interface" are extracted.Based on the analysis of the development trend and dynamic mechanism,combined with the spatial evolution characteristics and geographical features of the hilly terrain,the paper puts forward street and lane extension modes as "similar circle mode,main axis mode and multi-group mode" from three aspects of the street extension characteristics,the protection area division and the functional layout.And from the road classification,continuation pattern,inheritance of culture,protection interface and other aspects,the paper puts forward the method of street space construction,which provides a new strategy for the protection of historical streets and town construction.