Contrasting static versus dynamic-based typologies of land cover patterns in the Lisbon metropolitan area: Towards a better understanding of peri-urban areas

Peri-urban areas are usually a heterogeneous mosaic of rural, urban and natural systems which are quite dynamic across time. In this paper we contrast a static and a dynamic-based classification of local administrative units (LAU) in the Lisbon Metropolitan Area (LMA) to gain further insights onto the current land cover patterns and recent land cover changes in urban and peri-urban areas of the LMA. Using 16 landscape pattern indicators, we characterized the 211 LAU in the region contrasting a static (2006 data) and a dynamic-based (changes during the period 1990–2006) approach, and used cluster analyses to identify LAU typologies. Using the static approach we identified seven types of LAU, of which two were clearly urban, two could be considered rural, and three could be considered peri-urban. These latter could be distinguished among themselves by the landscape matrix type where urban areas were inserted. The dynamic-based approach yielded five types of LAU with specific trajectories in time, ranging from stable to highly dynamic. The frequency of the different dynamic typologies was not independent from the static ones, with typically urban areas being predominantly stable and rural areas having characteristic and exclusive trajectories of change. Peri-urban LAU were mostly moderately dynamic but shared a typology profile mixing highly dynamic LAU with moderately dynamic and stable ones. The combination of a static and dynamic view provides added value for the formulation of spatial planning policies in peri-urban areas.     

Activity patterns,socioeconomic status and urban spatial structure: what can social media data tell us?

ABSTRACT

Individual activity patterns are influenced by a wide variety of factors. The more important ones include socioeconomic status (SES) and urban spatial structure. While most previous studies relied heavily on the expensive travel-diary type data, the feasibility of using social media data to support activity pattern analysis has not been evaluated. Despite the various appealing aspects of social media data, including low acquisition cost and relatively wide geographical and international coverage, these data also have many limitations, including the lack of background information of users, such as home locations and SES. A major objective of this study is to explore the extent that Twitter data can be used to support activity pattern analysis. We introduce an approach to determine users’ home and work locations in order to examine the activity patterns of individuals. To infer the SES of individuals, we incorporate the American Community Survey (ACS) data. Using Twitter data for Washington, DC, we analyzed the activity patterns of Twitter users with different SESs. The study clearly demonstrates that while SES is highly important, the urban spatial structure, particularly where jobs are mainly found and the geographical layout of the region, plays a critical role in affecting the variation in activity patterns between users from different communities.     

基于客源地的聚类-ARIMA模型的短期旅游需求预测--以天津欢乐谷主题公园为例

大多数旅游需求预测研究是基于目的地游客总数或消费总量开展的,尚未按不同的旅游目的或客源地细分进行预测.以天津欢乐谷主题公园为案例地,选择2014年第40周到2015年第26周为研究时段,利用通信大数据,提出了一种面向客源地的聚类-ARIMA组合预测模型.通过对不同客源地的时序数据进行聚类,选取各类别中的代表性客源地分别构建ARIMA预测模型.结果表明:对欢乐谷主题公园各客源地分别建模与聚类后通过6个代表客源地建模得到的结果一致;后者可以降低80%的预测成本.该方法具有较高的预测精度和较低的计算成本,适合面向客源地的短期旅游需求预测,可为旅游目的地提供更具针对性的旅游需求管理、分析与决策支撑.     

DEM Fusion using a modified k-means clustering algorithm

Digital elevation models (DEMs) are a necessary dataset for modelling the Earth’s surface; however, all DEMs contain error. Researchers can reduce this error using DEM fusion techniques since numerous DEMs can be available for a region. However, the use of a clustering algorithm in DEM fusion has not been previously reported. In this study a new DEM fusion algorithm based on a clustering approach that works on multiple DEMs to exploit consistency in the estimates as indicators of accuracy and precision is presented. The fusion approach includes slope and elevation thresholding, k-means clustering of the elevation estimates at each cell location, as well as filtering and smoothing of the fusion product. Corroboration of the input DEMs, and the products of each step of the fusion algorithm, with a higher accuracy reference DEM enabled a detailed analysis of the effectiveness of the DEM fusion algorithm. The main findings of the research were: the k-means clustering of the elevations reduced the precision which also impacted the overall accuracy of the estimates; the number of final cluster members and the standard deviation of elevations before clustering both had a strong relationship to the error in the k-means estimates.     

秋季西沙非台风强降水天气形势分析

利用西沙永兴岛、珊瑚岛的日降水量资料、欧洲中期数值预报中心再分析资料,以及热带气旋最佳路径资料,统计分析了西沙地区降水的气候特征,并用REOF和K-means聚类相结合的合成分析方法,对9-10月该地区非台强降水过程的环流形势进行分类。结果表明:(1)西沙地区在12月到次年4月降水少而在5-11月降水多,降水量最多为9和10月;(2)9-10月西沙地区非台强降水过程的环流形势可分为西南季风槽型、季风槽与冷空气结合型和强冷空气型等三类,其中西南季风槽型主要出现在20世纪90年代的9月,强冷空气型主要出现在10月并在90年代以后明显增多,这主要与南海季风槽在90年代偏活跃,冷空气活动在90年代以后偏强有关。     

K-MEANS CLUSTERING FOR CLASSIFICATION OF THE NORTHWESTERN PACIFIC TROPICAL CYCLONE TRACKS

Based on the Joint Typhoon Warning Center (JTWC) best-track dataset between 1965 and 2009 and the characteristic parameters including tropical cyclone (TC) position, intensity, path length and direction, a method for objective classification of the Northwestern Pacific tropical cyclone tracks is established by using K-means Clustering. The TC lifespan, energy, active season and landfall probability of seven clusters of tropical cyclone tracks are comparatively analyzed. The characteristics of these parameters are quite different among different tropical cyclone track clusters. From the trend of the past two decades, the frequency of the western recurving cluster (accounting for 21.3% of the total) increased, and the lifespan elongated slightly, which differs from the other clusters. The annual variation of the Power Dissipation Index (PDI) of most clusters mainly depended on the TC intensity and frequency. However, the annual variation of the PDI in the northwestern moving then recurving cluster and the pelagic west-northwest moving cluster mainly depended on the frequency.     

水环境质量评价的灰色聚类法

运用灰色聚类法对甘肃金昌市地下水质进行了评价,并与模糊数学方法作了比较。结果表明灰色聚类法不仅具有模糊数学的优点,又弥补了其不完善之处。因此,用灰色聚类法评价水质,方法简便,结论更符合客观实际。     

Spherical panel clustering and its numerical aspects

In modern approximation methods, linear combinations in terms of (space localizing) radial basis functions play an essential role. Areas of application are numerical integration formulae on the unit sphere Ω corresponding to prescribed nodes, spherical spline interpolation and spherical wavelet approximation. The evaluation of such a linear combination is a time-consuming task, since a certain number of summations, multiplications and the calculation of scalar products are required. A generalization of the panel clustering method in a spherical setup is presented. The economy and efficiency of panel clustering are demonstrated for three fields of interest, namely upward continuation of the Earth's gravitational potential, geoid computation by spherical splines and wavelet reconstruction of the gravitational potential. Received: 1 October 1997 / Accepted: 1 April 1998     

Clustering stochastic point process model for flood risk analysis

Since the introduction into flood risk analysis, the partial duration series method has gained increasing acceptance as an appealing alternative to the annual maximum series method. However, when the base flow is low, there is clustering in the flood peak or flow volume point process. In this case, the general stochastic point process model is not suitable to risk analysis. Therefore, two types of models for flood risk analysis are derived on the basis of clustering stochastic point process theory in this paper. The most remarkable characteristic of these models is that the flood risk is considered directly within the time domain. The acceptability of different models are also discussed with the combination of the flood peak counted process in twenty years at Yichang station on the Yangtze river. The result shows that the two kinds of models are suitable ones for flood risk analysis, which are more flexible compared with the traditional flood risk models derived on the basis of annual maximum series method or the general stochastic point process theory. Received: September 29, 1997     

Space-time seismicity and earthquake swarms: Certain observations along the slow-spreading mid-Indian Ocean ridges

The slow spreading mid-Indian Ocean ridge system containing the Carlsberg, Central and Southwest Indian ridges is seismically very active. In the present study, a detailed analysis has been carried out of the data of earthquake sources along different ridge segments in order to investigate the spatial and temporal clustering patterns and to evaluate crustal processes related to the swarm occurrences along these ridges. The spatial and temporal clustering pattern of the recent earthquakes (1980–1990) pertaining to nine major spreading segments and eight fracture zones suggests that the events cluster in greater proportion along the spreading segments than along the fracture zones. We performed a systematic search of earthquake catalogue during the period 1964–1990 by examining the spatio-temporal hypocentral clusters in order to identify the swarm occurrences along these ridges. The search included eighteen prominent sequences, of which, thirteen were earthquake swarms. Except two, all other swarms were found to be occurring mainly on the spreading segments. The maximum magnitude observed in these swarms is m_b = 5.4 and have many events predominantly showing normal faulting mechanisms. The spatial disposition and temporal activity of the events in swarms is much similar to the foreshock-mainshock-aftershock sequences observed along the spreading rift valley zones. These characteristics help us to support that swarms along the slow spreading mid-Indian Ocean ridges are the result of extensional tectonic activity, leading to the development of the median valley topography, a mechanism similar to that proposed by Bergman and Solomon (1990) for the Mid-Atlantic Ridge.