Location-based social media data from different platforms such as Twitter and Flickr increasingly serve with their point-geocoded content as data sources for a variety of applications. The standard visualization method uses a derivation of point maps, which works well with a limited amount of data, but it suffers from weaknesses related to cluttering and overlapping, especially for sets of categories. We developed a new visualization method for categorical point data, called "Micro Diagrams", which uses small diagrams to show the percentages of categories and the spatial distribution. The processing steps to derive the micro diagrams start with aggregating the points in a regular grid structure, which is followed by the selection of the diagram type that represents the numerical proportions and the application of a size scaling function to show the amounts of data. Various parameterization options are discussed and the influence of the color selection is analyzed. Finally, a case study combined with a user test presents the strengths and limits of the micro diagram method.
Abstract. The starting point for developing a new map was defined by the requirements of the “MeinGrün” project (can be translated as ‘my green’ project). The aim is the development of a mobile app, which enables routing to urban areas, including suggestions for attractive places for different activities. A specific map style was designed to communicate information related to green spaces effectively and to make users excited about the topic of the project.Among other reasons, we also want to apply our knowledge on vector tile generation and use it in teaching. For the demonstration of our research on generalization, it is beneficial to offer a web map service because such a service allows illustrating developed methods and results. Finally, the experience enables us to train students in the design and development of customized styles for zoomable web maps.The aim is to build a map service with several zoom levels up to small scales using data from OpenStreetMap and NaturalEarth. For better adaptivity, it is aimed to offer the map as vector and raster tiles with the same style. Besides, making high-resolution raster tiles available for retina displays is considered as well. The rationale is that everyone can choose the appropriate method of delivery for different contexts of application. These requirements result in some technological challenges: provide vector and raster tiles at the same time and style, keep the computation time for an update, and generation low. For providing and delivering up to date data, on-the-fly map generalization has been implemented, e.g., scale-dependent selection, simplification, and aggregation of various features.Figure 1 shows our result, a map in warm colors, and a reduced information load for serving a reference map. The visualization of roads with a simple line is unique, but this was also the intension of the applied research project: the production of something unique and easy rememberable for the “MeinGrün” project. The hill-shading uses raster tiles while all other map features work with vector tiles.The data transformation from the OpenStreetMap format to the spatial PostgreSQL/PostGIS database has been applied with IMPOSM, a well-documented and efficient tool. GDAL is used to import the NaturalEarth data and doing some processing steps. PostgreSQL and its spatial extension PostGIS serve in many web-mapping projects as a data store and offer a wide range of options for processing data. After specified queries are applied, the t_rex software generates the vector tiles from the database, which are then packed as MBtiles using mbutil. Finally, Tileserver GL is used to serve vector and raster tiles, including further necessary additions such as style, sprites, and glyphs.To sum up, we already have a working service, which is available on our server with an ongoing blog about the project. Still, it is a work on progress project that needs further research and development. For example, the integration of Wikipedia/Wikidata information for selecting place by their importance, transliteration of no-Latin place names for a world-wide coverage, and more and better labeling of features. Now the map extent is scale depended and covers at low zoom levels the whole world. In contrast, the higher zoom levels are only available in Dresden and Heidelberg to match the requirements of the “MeinGrün” project but will be extended in the future.
In cartographic generalization, the selection is an often-used method to adjust information density in a map. This paper deals with methods for selecting point features for a specific scale with numerical attributes, such as population, elevation, or visitors. With the Label Grid approach and the method of Functional Importance, two existing approaches are described, which have not been published in the scientific literature so far. They are explained and illustrated in the method chapter for better understanding. Furthermore, a new approach based on the Discrete Isolation measure is introduced. It combines the spatial position and the attribute's value and is defined as the minimum distance to the nearest point with a higher value. All described selection methods are implemented and made available as Plugins named “Point selection algorithms” for QGIS. Based on this implementation, the three methods are compared regarding runtime, parameterization, legibility, and generalization degree. Finally, recommendations are given on which data and use cases the approaches are suitable. We see digital maps with multiple scales as the main application of those methods. The possibilities of labeling the selected points are not considered within the scope of this work.
<p><strong>Abstract.</strong> In recent years, the usage of zoomable maps strongly increased. The development of small and cheap electronic devices with wireless internet connection such as smartphones and tablets has made maps nowadays to a crucial part of everyday life. For the navigation and orientation, the user often uses zoomable maps (Muehlenhaus, 2014). Currently the technological development controls the map design and less cartographic design rules, which leads to the impress those current maps have a lower graphic quality. A sample for this trend is the new vector tile based maps, which offer the advantage of rotatable, multilingual maps build on one database (Martinelli and Roth, 2016).</p><p> There is a need for the development of cartographic design guidelines to guarantee consistent map readability over all zoom levels. The infinitely zoomable maps especially vector maps intensify this development. Analog maps had one specific scale, while a series of topographic maps were offered in manageable number of scales in comparison to OpenStreetMaps 20 zoom levels for raster tiles (Anon, 2019). Raster web maps had a number of predefined zoom levels, while vector maps offer the possibility of continuous zooming. This fact clarifies the requirement of research and development of rules for such types of maps.</p><p> A first important task for the fulfilment of this objective is the evaluation of a multi-scale map styles. For this task, we developed the concept of a multi-scale legend. This new tool should help cartographers and designer to create, modify and improve multi-scale map styles. It can help to explore existing map styles, identify inconsistencies and support the design process. We decided to use the legend due to the abstraction of the map style from map content. For visualization of the scale-dependencies for each feature in a row, the scale/zoom level changes in each column. In combination with other map features and zoom levels results a two-dimensional matrix showing the scale-dependent visualization. This legend matrix shows the map features in every zoom level, which allows reaching an overview of the symbolization of features over several scales. In this way, it is possible to check how consistent a map style is in one zoom level as well as over a set of zoom levels.</p><p> Figure 1 shows an example for a legend matrix using the OpenStreetMap Carto style: the representation of selected water bodies depending on the scale is illustrated. Streams and springs always occur together within the same zoom levels. In contrast to the rivers, the width of the streams remains nearly constant across the different scales. It is also visible that the color for the spring differs from the other water features. A multi-scale legend offers the possibility of grouping feature classes by topics (e.g. water bodies, vegetation and road network) as in the example. Other possibilities are geometry, color or occurrence in similar zoom levels. This can help in the search for errors, in the identification of breaks in the symbolization and in the development of continuous symbolization. The result is similar but more illustrative than the ScaleMaster (Brewer and Buttenfield, 2007, 2010), which is a diagram describing how feature classes are visualized depending from scale. Benefits of this legend are clarification of scale depended visualizations and the graphic implementation of design guidelines. A challenge is the implementation for different map styles due to the associated effort and the resulting sometimes very large overviews.</p><p> An on-going technological development takes place, wherefore cartographers should upgrade the design guidelines and methods for the production of current technological, well-looking maps. With the multi-scale legend, we provided a smart legend for a zoomable map. Nevertheless, these new ideas we have developed need more research and should always take the map purpose in account. Further, we would like to apply the multi-scale legend on existing map styles to reach more information about how these styles are working. In addition, we will further develop the multi-scale legend to a documentation of the creation of the map, showing how data is generalized and visualized.</p>
Abstract. Urban green spaces (UGSs) can provide important ecosystem services for citizens and their well-being. To make use of these services according to UGS user demands, urban residents, tourists, and city administrations should know where UGSs are located, what qualities they have and how to reach them on convenient routes. This paper presents a novel digital infrastructure which combines and fuses different data to map UGSs and their qualities, and makes this information available in a web app. The interactive information service of the app aims to support citizens to explore and search for suitable UGSs and to provide routing options to reach them based on their preferences. Via implicit and explicit feedback functions included in the app, further information on UGS users' preferences can be collected to enhance the overall knowledge basis, while respecting data privacy issues. The underlying data base consists primarily of open and volunteered geographic data, which allows for transferability to other cities. This paper describes the system design, its back-end and front-end components, as well as the process of development and deployment of the system in two pilot cities. Preliminary results of the piloting in the two cities are presented, focusing on user preferences for UGSs searches. The added value of the web app for city residents and the role of the newly gained knowledge for urban planning is discussed and reflected upon.
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