An exploratory analysis of usability of Flickr tags for land use/land cover attribution

This study explored the land use/land cover(LULC)separability by the machine-generated and user-generated Flickr photo tags(i.e.the auto-tags and the user-tags,respectively),based on an authoritative LULC dataset for San Diego County in the United States.Ten types of LULCs were derived from the authoritative dataset.It was observed that certain types of the reclassified LULCs had abundant tags(e.g.the parks)or a high tag density(e.g.the commercial lands),compared with the less populated ones(e.g.the agricultural lands).Certain highly weighted terms of the tags derived based on a term frequency–inverse document frequency weighting scheme were helpful for identifying specific types of the LULCs,especially for the commercial recreation lands(e.g.the zoos).However,given the 10 sets of tags retrieved from the corresponding 10 types of LULCs,one set of tags(all the tags located at one specific type of the LULCs)could not fully delineate the corresponding LULC due to semantic overlaps,according to a latent semantic analysis.

OpenStreetMap data quality enrichment through awareness raising and collective action tools——experiences from a European project

Nowadays,several research projects show interest in employing volunteered geographic information(VGI)to improve their systems through using up-to-date and detailed data.The European project CAP4Access is one of the successful examples of such international-wide research projects that aims to improve the accessibility of people with restricted mobility using crowdsourced data.In this project,OpenStreetMap(OSM)is used to extend OpenRouteService,a well-known routing platform.However,a basic challenge that this project tackled was the incompleteness of OSM data with regards to certain information that is required for wheelchair accessibility(e.g.sidewalk information,kerb data,etc.).In this article,we present the results of initial assessment of sidewalk data in OSM at the beginning of the project as well as our approach in awareness raising and using tools for tagging accessibility data into OSM database for enriching the sidewalk data completeness.Several experiments have been carried out in different European cities,and discussion on the results of the experiments as well as the lessons learned are provided.The lessons learned provide recommendations that help in organizing better mapping party events in the future.We conclude by reporting on how and to what extent the OSM sidewalk data completeness in these study areas have benefited from the mapping parties by the end of the project.

Routing through open spaces-A performance comparison of algorithms

Finding the shortest path through open spaces is a well-known challenge for pedestrian routing engines.A common solution is routing on the open space boundary,which causes in most cases an unnecessarily long route.A possible alternative is to create a subgraph within the open space.This paper assesses this approach and investigates its implications for routing engines.A number of algorithms(Grid,Spider-Grid,Visibility,Delaunay,Voronoi,Skeleton)have been evaluated by four different criteria:(i)Number of additional created graph edges,(ii)additional graph creation time,(iii)route computation time,(iv)routing quality.We show that each algorithm has advantages and disadvantages depending on the use case.We identify the algorithms Visibility with a reduced number of edges in the subgraph and Spider-Grid with a large grid size to be a good compromise in many scenarios.

The OpenStreetMap folksonomy and its evolution

The comprehension of folksonomies is of high importance when making sense of Volunteered Geographic Information(VGI),in particular in the case of OpenStreetMap(OSM).So far,only little research has been conducted to understand the role and the evolution of folksonomies in VGI and OSM,which is despite the fact that without a comprehension of the folksonomies the thematic dimension of data can hardly be used.This article examines the history of the OSM folksonomy,with the aim to predict its future evolution.In particular,we explore how the documentation of the OSM folksonomy relates to its actual use in the data,and we investigate the historical and future scope and granularity of the folksonomy.Finally,a visualization technique is proposed to examine the folksonomy in more detail.

Do people communicate about their whereabouts? Investigating the relation between user-generated text messages and Foursquare check-in places

The social functionality of places(e.g.school,restaurant)partly determines human behaviors and reflects a region’s functional configuration.Semantic descriptions of places are thus valuable to a range of studies of humans and geographic spaces.Assuming their potential impacts on human verbalization behaviors,one possibility is to link the functions of places to verbal representations such as users’postings in location-based social networks(LBSNs).In this study,we examine whether the heterogeneous user-generated text snippets found in LBSNs reliably reflect the semantic concepts attached with check-in places.We investigate Foursquare because its available categorization hierarchy provides rich a-priori semantic knowledge about its check-in places,which enables a reliable verification of the semantic concepts identified fromuser-generated text snippets.A latent semantic analysis is conducted on a large Foursquare check-in dataset.The results confirm that attached text messages can represent semantic concepts by demonstrating their large correspondence to the official Foursquare venue categorization.To further elaborate the representativeness of text messages,this work also performs an investigation on the textual terms to quantify their abilities of representing semantic concepts(i.e.,representativeness),and another investigation on semantic concepts to quantify how well they can be represented by text messages(i.e.,representability).The results shed light on featured terms with strong locational characteristics,as well as on distinctive semantic concepts with potentially strong impacts on human verbalizations.

Detecting repetitive structures on building footprints for the purposes of 3D modeling and reconstruction

Repetitive structures of a building share features in terms of geometries and appearance and,therefore,the 3D information for these structures can be transferred from one specification to another for the purpose of 3D modeling and reconstruction once they are identified as repetitive structures.In this paper,a novel approach is proposed for the detection of the repetitive structures specified by the polygons of a building’s footprints.Instead of directly operating on the polygon in 2D space,the polygon is converted into a bend angle function representation in 1D space,whereby an extrusion is represented as a closed polygon intersected by the x-axis and located above it,while an intrusion is represented as a closed polygon below the x-axis.In this way,a polygon of a footprint is decomposed into a number of extrusions and intrusions which can in turn be processed.The task of detecting any repetitive structures specified in a building’s footprints then becomes the task of clustering the intersected polygons in the bend angle function space.The extrusions/intrusions which can be placed in the same clusters can be regarded as repetitive structures.Experiments show that this proposed approach can detect repetitive structures with different sizes,orientations and complexities.

Completeness of citizen science biodiversity data from a volunteered geographic information perspective

Observations of living organisms by citizen scientists that are reported to online portals are a valuable source of information.They are also a special kind of volunteered geographic information(VGI).VGI data have issues of completeness,which arise from biases caused by the opportunistic nature of the data collection process.We examined the completeness of bird species represented in citizen science observation data from eBird and iNaturalist in US National Parks(NPs).We used approaches for completeness estimation which were developed for data from OpenStreetMap,a crowdsourced map of the world.First,we used an extrinsic approach,comparing species lists from citizen science data with National Park Service lists.Second,we examined two intrinsic approaches using total observation numbers in NPs and the development of the number of new species being added to the data-set over time.Results from the extrinsic approach provided appropriate completeness estimations to evaluate the intrinsic approaches.We found that total observation numbers are a good estimator of species completeness of citizen science data from US NPs.There is also a close relationship between species completeness and the ratio of new species added to observation data vs.observation numbers in a given year.

Open-data-driven embeddable quality management services for map-based web applications

Various map-centered web services facilitate citizens’lives.Webmap applications exist for many years already.Due to simplification and improvement of technologies supporting WebGIS,mapbased services become more popular and important nowadays.Data quality assurance for such services is a significant challenge.Since many of such applications intensively use open data,approaches focused on open solutions are required.This work proposes a data-quality concept,which is based on intrinsic and comparable approaches.OpenStreetMap(OSM)allows intrinsic data evaluation.Moreover,it is used as a reference dataset for quality assessment of public-sector-information Open Data layers.Equidistant point(EDP)-based statistics enables to filter out lowquality Open Data features.A data-type model carries out the inventory of OSM data.The comparison of raster web-map tile file sizes and calculation of a simplified data quality indicator make it possible to specify acceptable data quality levels.Embeddable instances of quality assurance web services incorporate data features with acceptable quality.This work provides all required software and data for the deployment of such services under liberal licenses.Concrete instructions allow users to adopt the proposed solutions for their platforms.Some generic use cases illustrate the advantages of the introduced shared web services.