A scientific delineation of geographical boundaries reflects the cognitive level of scientific abstraction and systematic analysis of the spatial variation of geographical objects and is a basic scientific issue of geography. From the perspective of earth system science, this study first explicates the core issues (e.g., basic concepts, scientific contents, and basic properties) of geographical boundaries. Based on the principles of scientificity and systematicness, we then classify geographical boundaries in terms of intrinsic mechanisms, extrinsic appearance and scientific attributes. Furthermore, this paper analyzes the mathematical connotation and representation methods of geographical boundaries, discusses the characteristics of and differences between traditional and modern methods for geographical boundary delineation. Finally, we present a framework for a “geographical boundary model” with an integration of qualitative, quantitative, and positioning methods. Focusing on geographical boundary (a basic theoretical problem in geography), this study engaged in concept definition and method analysis, with the findings enriching the theory and methodology of geographical information science. 相似文献
The agricultural regional type and function are the key theoretical issues in agricultural geography research. Gully agriculture in the Loess Plateau is a new regional type of agricultural system with the coupling development of the modern gully human-earth relationship. The study of its functional changes is of great practical significance for food security, rural revitalization and sustainable development of regional agriculture in the region of interest. This paper analyses the multifunctional change of gully agriculture in the Loess Plateau and its dynamic mechanism by using large-scale remote sensing data, topographic relief amplitude model, and spatial econometric model to understand internal implications for evolution differentiation at the basin level. The results show that: (1) The spatial concentration of production and supply function of agricultural products (APF) in the gully of the Loess Plateau gully is high, while the ecological conservation and maintenance function (ECF), employment and social security function (ESF), cultural heritage and leisure function (CRF) are relatively low. The four functions’ spatial distribution has revealed an apparent regularity. (2) APF has been significantly enhanced, which is mainly distributed in point clusters and strips in the farming and pastoral areas in northern Shaanxi to the Yanhe river basin. The high-value areas of ESF are clustered around the urbanized metropolitan circles and urban-rural staggered areas along the Great Wall. ECF is concentrated in areas with significant natural endowments and excellent ecological conditions. CRF is significantly higher in the municipal districts and the surrounding regional central cities. (3) There are noticeable differences in the gully agriculture regional function (GARF) evolution process due to the geographical environment and socio-economic development stages. In this regard, natural factors have tremendously affected APF, ESF, and ECF, while socio-economic factors greatly differ in the four functions. There are still differences in the driving mechanisms of modern gully agriculture evolution types; hence many critical policies in the Loess Plateau can directly affect the function evolution paths. The dynamic evolution of GARF can reflect the general law of rural human-earth system transition in gully areas, thereby providing policy ideas for high-quality development of agriculture in the Loess Plateau. 相似文献
Simultaneous measurements of the vertical magnetic field (VMF), three-dimensional electric field, ambient temperature, ambient relative humidity, particle mass concentration, and three-dimensional velocity are conducted during dust, haze, rain, snow, and thunderstorms. The hourly VMF variation (the rate of VMF increment and time increment with a 1-h time interval) is used to evaluate the disturbance level of the atmospheric magnetic field during the abovementioned weather conditions. There is no significant difference in the hourly VMF variations between hazy days and fair weather. However, the hourly VMF variations on dusty, rainy, snowy, and thunderstorm days differ from those in fair weather, implying that these weather conditions significantly affect the atmospheric magnetic field. On hazy days, although the haze particles are charged, the VMF does not change compared with in fair weather, which suggests that the horizontal electric field generated by haze particles is an irrotational field. On dusty and snowy days, the heterogeneity of the charge distribution forms a rotational horizontal electric field, which can induce the VMF to disturb the atmospheric magnetic field. During rain and thunderstorms, the hourly variation in the VMF is larger than in dust and snow, which can be attributed to the rotational horizontal electric field generated by raindrops and clouds. In addition, the hourly variation in the VMF in thunderstorms is one order of magnitude larger than that during days without thunderstorms, indicating that the VMF induced by the cumulonimbus cloud electric field is more significant than that in other weather conditions.
