Aim Spatial and temporal biases in species-occurrence data can compromise broad-scale biogeograph... more Aim Spatial and temporal biases in species-occurrence data can compromise broad-scale biogeographical research and conservation planning. Although spatial biases have been frequently scrutinized, temporal biases and the overall quality of species-occurrence data have received far less attention. This study aims to answer three questions: (1) How reliable are species-occurrence data for flowering plants in Africa? (2) Where and when did botanical sampling occur in the past 300 years? (3) How complete are plant inventories for Africa? Location Africa. Methods By filtering a publicly available dataset containing 3.5 million records of flowering plants, we obtained 934,676 herbarium specimens with complete information regarding species name, date and location of collection. Based on these specimens, we estimated inventory completeness for sampling units (SUs) of 25 km 3 25 km. We then tested whether the spatial distribution of well-sampled SUs was correlated with temporal parameters of botanical sampling. Finally, we determined whether inventory completeness in individual countries was related to old or recently collected specimens. Results Thirty-one per cent of SUs contained at least one specimen, whereas only 2.4% of SUs contained a sufficient number of specimens to reliably estimate inventory completeness. We found that the location of poorly sampled areas remained almost unchanged for half a century. Moreover, there was pronounced temporal bias towards old specimens in South Africa, the country that holds half of the available data for the continent. There, high inventory completeness stems from specimens collected several decades ago. Main conclusions Despite the increasing availability of species occurrence data for Africa, broad-scale biogeographical research is still compromised by the uncertain quality and spatial and temporal biases of such data. To avoid erroneous inferences, the quality and biases in species-occurrence data should be critically evaluated and quantified prior to use. To this end, we propose a quantification method based on inventory completeness using easily accessible species-occurrence data.
Today, one's disposes of large datasets composed of thousands of geographic objects. However, for... more Today, one's disposes of large datasets composed of thousands of geographic objects. However, for many processes, which require the appraisal of an expert or much computational time, only a small part of these objects can be taken into account. In this context, robust sampling methods become necessary. In this paper, we propose a sampling method based on clustering techniques. Our method consists in dividing the objects in clusters, then in selecting in each cluster, the most representative objects. A case-study in the context of a process dedicated to knowledge revision for geographic data generalisation is presented. This case-study shows that our method allows to select relevant samples of objects.
A classic approach in automated generalisation consists in formalising generalisation as an optim... more A classic approach in automated generalisation consists in formalising generalisation as an optimisation problem: the goal is to find a state of the data that maximises an evaluation function that is supposed to assess the data generalisation state, according to user's need. A key ...
Lecture Notes in Geoinformation and Cartography, 2014
This chapter reviews recent development in terrain generalisation. The focus is put on cartograph... more This chapter reviews recent development in terrain generalisation. The focus is put on cartographic generalisation where the terrain representation is adapted with consideration to the aesthetics and legibility of the map for a specific purpose. Generalisation methods apply to traditional terrain representations (spot heights, contours, hypsometric colours, shaded relief) but also to grid and triangulated surface generalisation. First, issues related to relief representation on maps at different scales are discussed. As generalisation requires knowledge about the terrain morphology, several approaches focusing on the classification of terrain features according to morphometric or topological criteria were developed. Cartographic generalisation methods are reviewed with consideration to conflicts between terrain representations and other object type data on the map. In the second part, three case studies illustrating previous developments are presented. First, a generalisation method for hypsometric map production is described where important valleys and mountain ridges are accentuated to improve the representation. Second, a method selecting features represented by isobaths and answering specific constraints of nautical charts is presented. The third case study is a generalisation method which takes into account other objects of the map such as buildings and rivers.
In this part, some application cases of the AGENT and CartACom prototypes will be presented. We w... more In this part, some application cases of the AGENT and CartACom prototypes will be presented. We will show some situations transformed without taking care of the background themes.
La généralisation cartographique consiste à simplifier les objets représentés sur une carte afin ... more La généralisation cartographique consiste à simplifier les objets représentés sur une carte afin d'en améliorer la lisibilité. Des travaux antérieurs se sont attachés à mettre au point des modèles de généralisation automatiques basés sur une approche agent: les objets cartographiques sont des agents qui se généralisent en s'appliquant des traitements géométriques. Plusieurs niveaux, appelés niveaux micro et meso, sont considérés. Notre objectif est de compléter ces modèles en permettant de gérer des transformations plus continues, comme des déformations. Le modèle que nous proposons s'appuie sur la recherche d'un équilibre entre des contraintes élastiques. Ces contraintes s'appliquent à un niveau particulaire des objets que nous appelons niveau « sub-micro ». Nous appliquons cette méthode à la déformation d'un type d'objets particulier: les objets champs.
Dans cet article, nous nous intéressons à la rela-tion existant entre le relief et le réseau hydr... more Dans cet article, nous nous intéressons à la rela-tion existant entre le relief et le réseau hydrogra-phique. Cette relation est particulièrement importan-te : dans le monde réel, les cours d'eau s'écoulent sur le relief. Beaucoup de cours d'eau se trouvent dans des vallées (ou ...
La simulation des évolutions des villes suppose une certaine compréhension et une modélisation de... more La simulation des évolutions des villes suppose une certaine compréhension et une modélisation des lois qui gouvernent les dynamiques urbaines. L'approche présentée dans ce papier utilise un système multi-agent pour modéliser les propriétés auto-organisatrices des systèmes complexes urbains et vise à fournir un outil permettant d'étudier les évolutions des systèmes modélisés. Le système multi-agent proposé comporte une hiérarchie d'agents topographiques (e.g. les bâtiments, routes, cours d'eau, îlots) qui peuvent être construits, modifiés, fusionnés, découpés, restructurés et détruits au cours du temps. Le comportement de chaque agent est contrôlé par un ensemble de règles d'évolution, de contraintes et d'actions associées.
De nombreux modèles de généralisation de données géographiques ont contribué à améliorer l'au... more De nombreux modèles de généralisation de données géographiques ont contribué à améliorer l'automatisation de ce processus particulièrement complexe. Ce papier s'intéresse au modèle à base d'agents GAEL, qui fournit un moyen générique d'effectuer des déformations continues d'objets. Le principe de ce modèle de déformation est de rendre les objets déformables en les décomposant en petits objets contraints (segments, triangles, etc.), la déformation étant obtenue en équilibrant ces contraintes. En fonction du choix de ces contraintes, un objet peut se déformer de différentes façons. Cet article illustre comment le modèle peut être adapté à trois opérations de généralisation : l'équarrissage de bâtiment, le déplacement de courbes de niveau et le déplacement de bâtiment. Nous discuterons ensuite les notions de généricité et de facilité d'adaptation des modèles de généralisation, et proposerons des points méthodologiques pour améliorer ces caractéristiques impo...
The European Atlas of the Seas is a web-based information system aimed at the general public, but... more The European Atlas of the Seas is a web-based information system aimed at the general public, but it is also capable of supporting selected nonspecialist professionals in addressing environmental issues, human activities, and policies related to the coast and sea. It includes a collection of maps and associated fact sheets based on data originating primarily from the European Commission and its agencies, which present a snapshot of key natural and socio-economic elements of the coastal and marine regions of the European Union. It provides a suite of basic instruments for map analysis and data combination to derive ad hoc maritime indicators.
This chapter reviews recent development in terrain generalisation. The focus is put on cartograph... more This chapter reviews recent development in terrain generalisation. The focus is put on cartographic generalisation where the terrain representation is adapted with consideration to the aesthetics and legibility of the map for a specific purpose. Generalisation methods apply to traditional terrain representations (spot heights, contours, hypsometric colours, shaded relief) but also to grid and triangulated surface generalisation. First, issues related to relief representation on maps at different scales are discussed. As generalisation requires knowledge about the terrain morphology, several approaches focusing on the classification of terrain features according to morphometric or topological criteria were developed. Cartographic generalisation methods are reviewed with consideration to conflicts between terrain representations and other object type data on the map. In the second part, three case studies illustrating previous developments are presented. First, a generalisation method for hypsometric map production is described where important valleys and mountain ridges are accentuated to improve the representation. Second, a method selecting features represented by isobaths and answering specific constraints of nautical charts is presented. The third case study is a generalisation method which takes into account other objects of the map such as buildings and rivers.
Aim Spatial and temporal biases in species-occurrence data can compromise broad-scale biogeograph... more Aim Spatial and temporal biases in species-occurrence data can compromise broad-scale biogeographical research and conservation planning. Although spatial biases have been frequently scrutinized, temporal biases and the overall quality of species-occurrence data have received far less attention. This study aims to answer three questions: (1) How reliable are species-occurrence data for flowering plants in Africa? (2) Where and when did botanical sampling occur in the past 300 years? (3) How complete are plant inventories for Africa? Location Africa. Methods By filtering a publicly available dataset containing 3.5 million records of flowering plants, we obtained 934,676 herbarium specimens with complete information regarding species name, date and location of collection. Based on these specimens, we estimated inventory completeness for sampling units (SUs) of 25 km 3 25 km. We then tested whether the spatial distribution of well-sampled SUs was correlated with temporal parameters of botanical sampling. Finally, we determined whether inventory completeness in individual countries was related to old or recently collected specimens. Results Thirty-one per cent of SUs contained at least one specimen, whereas only 2.4% of SUs contained a sufficient number of specimens to reliably estimate inventory completeness. We found that the location of poorly sampled areas remained almost unchanged for half a century. Moreover, there was pronounced temporal bias towards old specimens in South Africa, the country that holds half of the available data for the continent. There, high inventory completeness stems from specimens collected several decades ago. Main conclusions Despite the increasing availability of species occurrence data for Africa, broad-scale biogeographical research is still compromised by the uncertain quality and spatial and temporal biases of such data. To avoid erroneous inferences, the quality and biases in species-occurrence data should be critically evaluated and quantified prior to use. To this end, we propose a quantification method based on inventory completeness using easily accessible species-occurrence data.
Today, one's disposes of large datasets composed of thousands of geographic objects. However, for... more Today, one's disposes of large datasets composed of thousands of geographic objects. However, for many processes, which require the appraisal of an expert or much computational time, only a small part of these objects can be taken into account. In this context, robust sampling methods become necessary. In this paper, we propose a sampling method based on clustering techniques. Our method consists in dividing the objects in clusters, then in selecting in each cluster, the most representative objects. A case-study in the context of a process dedicated to knowledge revision for geographic data generalisation is presented. This case-study shows that our method allows to select relevant samples of objects.
A classic approach in automated generalisation consists in formalising generalisation as an optim... more A classic approach in automated generalisation consists in formalising generalisation as an optimisation problem: the goal is to find a state of the data that maximises an evaluation function that is supposed to assess the data generalisation state, according to user's need. A key ...
Lecture Notes in Geoinformation and Cartography, 2014
This chapter reviews recent development in terrain generalisation. The focus is put on cartograph... more This chapter reviews recent development in terrain generalisation. The focus is put on cartographic generalisation where the terrain representation is adapted with consideration to the aesthetics and legibility of the map for a specific purpose. Generalisation methods apply to traditional terrain representations (spot heights, contours, hypsometric colours, shaded relief) but also to grid and triangulated surface generalisation. First, issues related to relief representation on maps at different scales are discussed. As generalisation requires knowledge about the terrain morphology, several approaches focusing on the classification of terrain features according to morphometric or topological criteria were developed. Cartographic generalisation methods are reviewed with consideration to conflicts between terrain representations and other object type data on the map. In the second part, three case studies illustrating previous developments are presented. First, a generalisation method for hypsometric map production is described where important valleys and mountain ridges are accentuated to improve the representation. Second, a method selecting features represented by isobaths and answering specific constraints of nautical charts is presented. The third case study is a generalisation method which takes into account other objects of the map such as buildings and rivers.
In this part, some application cases of the AGENT and CartACom prototypes will be presented. We w... more In this part, some application cases of the AGENT and CartACom prototypes will be presented. We will show some situations transformed without taking care of the background themes.
La généralisation cartographique consiste à simplifier les objets représentés sur une carte afin ... more La généralisation cartographique consiste à simplifier les objets représentés sur une carte afin d'en améliorer la lisibilité. Des travaux antérieurs se sont attachés à mettre au point des modèles de généralisation automatiques basés sur une approche agent: les objets cartographiques sont des agents qui se généralisent en s'appliquant des traitements géométriques. Plusieurs niveaux, appelés niveaux micro et meso, sont considérés. Notre objectif est de compléter ces modèles en permettant de gérer des transformations plus continues, comme des déformations. Le modèle que nous proposons s'appuie sur la recherche d'un équilibre entre des contraintes élastiques. Ces contraintes s'appliquent à un niveau particulaire des objets que nous appelons niveau « sub-micro ». Nous appliquons cette méthode à la déformation d'un type d'objets particulier: les objets champs.
Dans cet article, nous nous intéressons à la rela-tion existant entre le relief et le réseau hydr... more Dans cet article, nous nous intéressons à la rela-tion existant entre le relief et le réseau hydrogra-phique. Cette relation est particulièrement importan-te : dans le monde réel, les cours d'eau s'écoulent sur le relief. Beaucoup de cours d'eau se trouvent dans des vallées (ou ...
La simulation des évolutions des villes suppose une certaine compréhension et une modélisation de... more La simulation des évolutions des villes suppose une certaine compréhension et une modélisation des lois qui gouvernent les dynamiques urbaines. L'approche présentée dans ce papier utilise un système multi-agent pour modéliser les propriétés auto-organisatrices des systèmes complexes urbains et vise à fournir un outil permettant d'étudier les évolutions des systèmes modélisés. Le système multi-agent proposé comporte une hiérarchie d'agents topographiques (e.g. les bâtiments, routes, cours d'eau, îlots) qui peuvent être construits, modifiés, fusionnés, découpés, restructurés et détruits au cours du temps. Le comportement de chaque agent est contrôlé par un ensemble de règles d'évolution, de contraintes et d'actions associées.
De nombreux modèles de généralisation de données géographiques ont contribué à améliorer l'au... more De nombreux modèles de généralisation de données géographiques ont contribué à améliorer l'automatisation de ce processus particulièrement complexe. Ce papier s'intéresse au modèle à base d'agents GAEL, qui fournit un moyen générique d'effectuer des déformations continues d'objets. Le principe de ce modèle de déformation est de rendre les objets déformables en les décomposant en petits objets contraints (segments, triangles, etc.), la déformation étant obtenue en équilibrant ces contraintes. En fonction du choix de ces contraintes, un objet peut se déformer de différentes façons. Cet article illustre comment le modèle peut être adapté à trois opérations de généralisation : l'équarrissage de bâtiment, le déplacement de courbes de niveau et le déplacement de bâtiment. Nous discuterons ensuite les notions de généricité et de facilité d'adaptation des modèles de généralisation, et proposerons des points méthodologiques pour améliorer ces caractéristiques impo...
The European Atlas of the Seas is a web-based information system aimed at the general public, but... more The European Atlas of the Seas is a web-based information system aimed at the general public, but it is also capable of supporting selected nonspecialist professionals in addressing environmental issues, human activities, and policies related to the coast and sea. It includes a collection of maps and associated fact sheets based on data originating primarily from the European Commission and its agencies, which present a snapshot of key natural and socio-economic elements of the coastal and marine regions of the European Union. It provides a suite of basic instruments for map analysis and data combination to derive ad hoc maritime indicators.
This chapter reviews recent development in terrain generalisation. The focus is put on cartograph... more This chapter reviews recent development in terrain generalisation. The focus is put on cartographic generalisation where the terrain representation is adapted with consideration to the aesthetics and legibility of the map for a specific purpose. Generalisation methods apply to traditional terrain representations (spot heights, contours, hypsometric colours, shaded relief) but also to grid and triangulated surface generalisation. First, issues related to relief representation on maps at different scales are discussed. As generalisation requires knowledge about the terrain morphology, several approaches focusing on the classification of terrain features according to morphometric or topological criteria were developed. Cartographic generalisation methods are reviewed with consideration to conflicts between terrain representations and other object type data on the map. In the second part, three case studies illustrating previous developments are presented. First, a generalisation method for hypsometric map production is described where important valleys and mountain ridges are accentuated to improve the representation. Second, a method selecting features represented by isobaths and answering specific constraints of nautical charts is presented. The third case study is a generalisation method which takes into account other objects of the map such as buildings and rivers.
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Papers by Julien Gaffuri