Thiessen Polygons

mapping in relation with informal settlement upgrading based on information gathered from the residents of the informal settlement. Furthermore, the application of GIS spatial analysis in different informal settlement problems is demonstrated. This research outlines the investigation of mapping and spatial analysis in Informal settlements upgrading using GIS, making use of five different analysis methods: Buffer analysis, thematic mapping, Thiessen polygons, distance mapping and Multi Criteria Evaluation. The case study area is Monwabisi Park in Cape Town and the data was collected by Violence Prevention through Urban Upgrading (VPUU). The study has revealed that the use of indigenous knowledge in GIS analysis for upgrading could be very valuable in making scientific and alternate decision during informal settlement upgrading process.

Geographical Information Systems (GIS) are powerful tools in the field of invasive species management. GIS can be used to create potential distribution maps for all manner of taxa, including plants, animals, and diseases. GIS also performs well in the early detection and rapid assessment of invasive species. Here, we used GIS applications to investigate species richness and invasion patterns in fish in the United States (US) at the 6-digit Hydrologic Unit Code (HUC) level. We also created maps of potential spread of the cane toad (Bufo marinus) in the southeastern US at the 8-digit HUC level using regression and environmental envelope techniques. Equipped with this potential map, resource managers can target their field surveys to areas most vulnerable to invasion. Advances in GIS technology, maps, data, and many of these techniques can be found on websites such as the National Institute of Invasive Species Science (www.NIISS.org). Such websites provide a forum for data sharing and analysis that is an invaluable service to the invasive species community.

Abstract— The estimation of areal rainfall is an important part of solving various hydrological problems utilizing rainfall-runoff and other models. Traditionally used Thiessen polygons (TP) method proved to be inaccurate mainly in mountainous areas and in catchments with insufficient number of rainfall gauges. One of the alternative to this method is an inverse distance weighting (IDW) method giving better estimates of areal rainfall even on places with rugged orography. However, this and similar methods are far less efficient than the simple TP method restraining its use to tasks where computational efficiency is not important. In this study a new algorithm accelerating the traditional IDW method is proposed and applied to three mountainous catchments situated in the central part of Slovakia. The method is compared with traditional IDW and TP methods in terms of both computational efficiency and estimated values. The results showed that while the new method gives the same results as the traditional IDW method it is far more efficient when the computational time was in all three catchments reduced by more than 96%.

RÉSUMÉ – La grande majorité des reliefs de la région du Sartenais, au sud-ouest de la Corse, a connu une occupation au cours de l’âge du Bronze et/ou de l’âge du Fer. Ces gisements ont, pour la plupart, été l’objet de sondages ou de prospections superficielles menés anciennement (1956-1975) par R. Grosjean et son équipe. Il a précédemment été possible, grâce à l’analyse de l’intégralité des mobiliers disponibles, de proposer une chronologie générale de l’évolution des formes de l’occupation des sols dans cette partie de l’île entre Bronze ancien et fin du premier âge du Fer. On se propose ici de poursuivre cette réflexion sur un champ d’investigation plus théorique au travers de postulats et schémas paléodémographiques et territoriaux jusqu’ici surtout développés par les écoles anglo-saxonnes mais depuis quelques années déjà testées en contexte méditerranéen. L’étude met en évidence la complexité des formes de l’emprise protohistorique sur le Sartenais, tant sur les échelles chronologiques que spatiales.

ABSTRACT – The reliefs of the Sartene region, located in south-west Corsica, were occupied, for the most part, during the Bronze and/or Iron Age. Between 1956 and 1975, R. Grosjean and his team surveyed most of these settlements through surface analysis. The study of all existent dwellings permitted to date the population dynamics of the region between Early Bronze and the beginning of the Iron Age. This paper is aimed at presenting the results of a follow-up study of the settlements, based on theoretical frameworks developed by the British school and applied to Mediterranean contexts in the last few years. This theoretical investigation allowed highlighting both the chronological and spatial complexity of proto-historic grasp in the region.

RIASSUNTO – La maggior parte dei rilievi della regione di Sartene, nel sud-ovest della Corsica, fu occupata durante l’età del Bronzo e/o l’età del Ferro. Durante gli anni 1956-1975, la maggior parte di questi insediamenti fu oggetto di sondaggi o prospezioni  superficiali diretti da R. Grosjean e dalla sua équipe. L’analisi della totalità delle strutture abitative ancora esistenti ha permesso di proporre un’ipotesi cronologica dell’evoluzione delle forme di occupazione di questi territori tra il Bronzo antico e la fine della prima età del Ferro. In questa sede si intende proseguire l’indagine sugli abitati a partire da un piano più teorico, basato su postulati paleodemografici e territoriali sviluppati dalla scuola anglosassone e applicati a contesti mediterranei negli ultimi anni. Tale indagine ha permesso di evidenziare la complessità delle forme di influenza protostorica nel Sartenais, da un punto di vista sia cronologico, sia spaziale.

The nearly complete list of Medieval settlements in a study area of the Bergisches Land, Germany, and a historical map of 1715 form the basis for analysing the settlement pattern of Medieval and early modern farms in this rural region. Only few archaeological remains of pre-Medieval periods have been recorded in this hilly study area with lots of small streams and at best moderately fertile soils, so most probably the population and the number of farms increased considerably during the Middle Ages. Settlement sizes (e.g. one, two, or three farms, hamlets, or villages with a church) are shown on the early 18th century map depicting nearly all Medieval settlements known from historical sources as well as a small portion of additional settlements. This study tries to retrodict likely settlement locations in this rural area, i.e. to identify the main factors governing the location of farms and villages. This is an unusual task due to the dense distribution of these locations. Several possible factors for settlement location are tested, and a retrodictive model combining relevant variables is presented. The analysis indicates that some variables with strong retrodictive power do not apply for single farmsteads. The landscape attributes identifying possible settlement locations tell only part of the story. Additional analysis is required to identify the distribution of the settlements with respect to their neighbours, such as regular distances between settlements of similar sizes as proposed by Christaller’s Central Place Theory. Least-cost Thiessen territories are calculated for all settlements on the historical map of 1715. It is shown that the Thiessen territory size depends on the settlement size and this indicates that hardly any space is left for additional settlements.

Forest regeneration is a spatial multifaceted process with numerous unknown variables. The individual area or the area potentially available (APA) to an individual plant embodies an idea widely used in population ecology but it has fewer applications in forest research. It was used a Voronoi/ Thiessen tessellation in order to determine the individual area of each sapling. The study was conducted in a naturally regenerated area; using data collected from over seven thousands saplings positioned in a network of permanent rectangular sampling plots. The Voronoi/ Thiessen polygons were used to characterize spatial pattern of sapling distribution as well as the competition relations between the individuals. It is obvious that, at least from the mathematically point of view, the Voronoi tessellation represents one of the best solutions to determine neighbouring competitors of a tree. There were studied the correlations between APA values and the main biometrical attributes, height growth and competition indices. Furthermore, it is shown that APA coefficient of variation is a straight-forward indicator with positive results as an indicator of spatial pattern. The statistical significance of this indicator was evaluated by comparing the results with the values of a 95% confidence envelope generated by Monte-Carlo simulations. Two practical software tools were produced using Visual Basic (VORONOI and ARIA VORONOI) in order to simplify the analyses.

It is a typical Mediterranean phenomenon that modern cities are built on top of ancient cities. Snapshots of
this palimpsest are viewed sometimes during the implementation of construction projects, primarily building
permits, which involve soil removal and extensive digging. The present application focuses on Patras, Greece
and makes use of a set of dig reports dating between 2004 and 2008, in which the absence or presence of
archaeological deposits is reported. It is considered whether archaeological and non-archaeological
excavations can provide a quick and functional way to record the archaeological palimpsest buried
underneath modern cities and for this reason Voronoi tessellation, conventional statistics and spatial
analysis are applied. Their predictive strength is tested and a digital map of the potentially archaeological
territory in Patras is produced. The results are then compared with the known archaeological profile of the
city and their implications for cultural heritage management and urban planning are discussed.

For part of Bergisches Land east of Cologne, Germany, the maps by Ploennies finished in 1715 AD and the accompanying text provide detailed data for testing approaches used in archaeology for determining the boundaries of agrarian production. The historical maps indicate the settlement sizes ranging from single farmsteads to towns with walls. In 1715 AD the towns were quite small and the economy in this rural area relied mostly on agriculture (oats and livestock). The boundaries of agrarian production can be estimated by applying methods for allocating farmland territories to the settlement locations. The methods discussed are site catchments, retrodictive modelling for neighbourhoods, Thiessen polygons and approaches based on the distances between neighbouring settlement locations. With the exception of retrodictive modelling for neighbourhoods, two variants of the approaches are applicable, either resting on straight-line or least-cost distances.

La estimación del valor esperado de una función sobre áreas geográficas es un problema que data de tiempo atrás. Hasta principios del siglo XX el método más común solía ser calcular la media aritmética de las medidas obtenidas en el campo, ignorando su posición geométrica. En 1911, Thiessen introdujo una nueva forma de cálculo que asignaba a cada punto de medición un peso relativo al área de influencia, que tenía en cuenta indirectamente la proximidad entre datos. En 1949, Quenouville crea, en otro contexto, el método de jackknife que se utiliza para estimar el sesgo y la desviación estándar. En 1979, Efron inventa el método de bootstrap que, entre otras cosas, es apropiado para estimar el valor esperado de una población así como su intervalo de confianza (IC). Si bien el método de Thiessen lleva usándose hace más de un siglo, no se han encontrado estudios sistemáticos que comparen su eficacia frente al método anterior ni frente a variantes posteriores como jackknife o bootstrap. Es...

Geographical Information Systems (GIS) are powerful tools in the field of invasive species management. GIS can be used to create potential distribution maps for all manner of taxa, including plants, animals, and diseases. GIS also performs well in the early detection and rapid assessment of invasive species. Here, we used GIS applications to investigate species richness and invasion patterns in fish in the United States (US) at the 6-digit Hydrologic Unit Code (HUC) level. We also created maps of potential spread of the cane toad (Bufo marinus) in the southeastern US at the 8-digit HUC level using regression and environmental envelope techniques. Equipped with this potential map, resource managers can target their field surveys to areas most vulnerable to invasion. Advances in GIS technology, maps, data, and many of these techniques can be found on websites such as the National Institute of Invasive Species Science (www.NIISS.org). Such websites provide a forum for data sharing and analysis that is an invaluable service to the invasive species community.

The catchment, or catchment area, is the area associated with a segment of a drainage network. Surface runoff in a catchment flows into the associated network segment. Catchment area is commonly used for estimating watershed parameters, such as upstream drainage area, flood frequency, or surface-water flow. Hydrologic analyses require relatively accurate catchment area estimates to furnish substantive conclusions. Conversely, alternative uses for catchment area may not require such precise estimates. Estimation of catchment areas using Thiessen polygons around evenly spaced points along network features is a rapid and computationally simple approach when compared to the alternative of deriving catchments from an elevation model; however, Thiessen-estimated catchments do not precisely follow the ridgelines of surface models and only provide approximate subdivisions of the watershed. This paper assesses the accuracy of Thiessen-derived catchment area estimates for several drainage net...