Addressing VGI Case Study

8/3/2019 Addressing VGI Case Study

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Article under Review for the International Journal of Spatial Data InfrastructuresResearch, Special Issue GSDI-11, submitted 2009-03-01

Addressing vagueness inVolunteered Geographic Information (VGI)

A case study

Bertrand De LonguevilleEuropean Commission Joint Research Centre

Institute for Environment & SustainabilityIspra, Italy

Email: [email protected]

Nicole Ostlnder

European Commission Joint Research CentreInstitute for Environment & Sustainability

Ispra, ItalyEmail: [email protected]

Carina KeskitaloDepartment of Social and Economic Geography

Ume University, SwedenEmail: [email protected]

Abstract

The stakeholders that are directly affected by the climate change might becomean invaluable source of information if their perceptions are shared with thegeneral public and the scientific community. Such Volunteered GeographicInformation (VGI) about environmental phenomena have however a certaindegree of vagueness, as they describe only a spatiotemporal and thematicsnapshot of the entire phenomenon. To reconcile vagueness of stakeholdersperception of environmental phenomenon with the crisp objects vision of currentVGI, we propose a hybrid strategy, combining an Open Gazetteer approach, andthe concept of Degree of Truth. On this basis, we describe eVGI, an innovativeweb application based on a service-oriented architecture. We implemented eVGIas a prototype, addressing a real-world case study implying stakeholders from

forestry, fishing and reindeer husbandry sectors in the Barents region.

Keywords: VGI, vagueness, climate change, stakeholder perceptions, webservices

This work is licensed under the Creative Commons Attribution-Noncommercial Works 3.0 License.

To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-nd/3.0/ or send aletter to Creative Commons, 543 Howard Street, 5th Floor, San Francisco, California, 94105, USA


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1. INTRODUCTION

The environmental changes that are referred to using the term climate changeare expected to affect our environment exceedingly. How these changes mightlook like and which will be the resulting impacts on our society are questions thatare continuously addressed in todays research. Recently published and widelydiscussed were e.g. the results of the Stern Reviewon the Economics of ClimateChange(Stern, 2007) and the IPCC Fourth Assessment Report(AR4) (Anisimovet al., 2007) available from IPCC (2007). Particularly the latter points out that, inorder to increase our understanding of climate change and the resulting impacts,stakeholder perceptions and local knowledge are an invaluable source of

information, if shared with the general public and the scientific community.

With the recent developments in Web technology, which are often summarizedas Web 2.0, the possibilities to share information obtained an entirely new quality:being mere information users in the past, a growing number of internet users nowvoluntarily share their knowledge and experience with other internet users. Theycreate what is called user-generated content (Craglia et al., 2008). One of themost popular products of such an activity is Wikipedia, the free multilingual onlineencyclopaedia. If, however, user-generated information is not only factual butbears a distinct spatiotemporal component, one speaks about VolunteeredGeographic Information, VGI for short (cf. Goodchild, 2007).

When we are dealing with climate change, VGI has a great potential: beyondbeing mere observers of environmental changes, stakeholders can link thesechanges to the impacts that they experience. Goodchild (2007) goes as far ascomparing stakeholders (or in fact, all citizens) to a new type of sensor networkwhere each citizen is a sensor that is [...] equipped with some working subset ofthe five senses and with the intelligence to compile and interpret what theysense, and each free to rove the surface of the planet. Particularly if they work insectors that rely on natural resources, citizens can provide valuable informationby applying local and sectoral knowledge (IPCC, 2007; Keskitalo, 2008).

The research presented in this paper focuses on a particular type of information:

stakeholder perceptions in form of testimonials that describe environmentalphenomena in a spatial, temporal and thematic manner and the resulting impactson their sector and way of life. This research is based on a real-world case studyin the Barents region in the European north. It was initiated in the EU-funded 5thframework project BALANCE1 and continued after the project ended in 2006:

1BALANCE stands for Global Change Vulnerabilities in the Barents Region: Linking Arctic Natural

Resources, Climate Change and Economies. BALANCE was supported by the fifth framework


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over the last years, actors from the forestry, fishing and reindeer husbandrysectors in the Barents region have been interviewed concerning their perceptionof environmental changes linked to climate change, and how these changesimpact them according to their experience on the field (Keskitalo, 2008).

While many of todays VGI systems describe VGI on man-made objects, such asstreets, single houses, cities, etc., systems for capturing VGI on environmentalphenomena are sparse (Rinner et al., 2008). In order to support research onclimate change through VGI we therefore aim at building such a system thatallows capturing stakeholder perceptions for the given case study. Suchperceptions have a spatial, a temporal and a thematic component. In this paperwe make the first steps towards such a system by analyzing how the

stakeholders in the case study describe the geographic location of environmentalphenomena and formulate the requirements for capturing such information.

Popular VGI systems like OpenStreetMap and WikiMapia inherit the object-oriented vision of geographic information, implying a certain spatial precision.Depending on the type of VGI that is expressed, the spatial precision mightindeed be high. For example if the provided information marks an addresses (myhouse or my favourite coffee bar) or has been created using a GPS device (mystreet) (Goodchild, 2007). However peoples perceptions of environmentalphenomena might not correspond to a known address. Or they might themselvesbe unsure about the extent of the environmental phenomenon they witnessed, astheir perception is recovered from memory, or they perceived only part of theentire phenomenon. In other words, their perceptions might be geographicallyvague. Thus, when it comes to existing VGI systems there turns out to be a lackof how to express such spatial vagueness, both when the information is enteredby one stakeholder, and when it is browsed and displayed by others.

Motivated by the above, we formulate the following research question to beaddressed in this paper: How can stakeholders perception of environmentalphenomena be integrated with the current vision of VGI? In order to address thisissue we suggest a hybrid strategy by combining an open gazetteer approach(Jones et al., 2008), and the concept of degree of truth(Fisher, 2000). The opengazetteerapproach permits users to locate events using their own words and

reference system. The concept of degree of truthincludes elements of the fuzzysets theory in the web based VGI system to reflect uncertainty of a givenlocalization. As a proof-of concept we design a web based system that cancapture, store and portray this volunteered and vague geographic information, toeffectively capture stakeholder testimonials on climate change. The web based

programme of the European Commission, within the Programme on Energy, Environment andSustainable Development [EVK2-2002-00169].


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system will be applied for an ongoing study of forestry, reindeer husbandry andtourism in selected locations in northern Sweden.

The remainder of paper is structured as follows: In section 2 we describe theconcepts and technologies that underlie our research. We then analyze thestakeholder perceptions collected in a qualitative stakeholder study (section 3) toidentify how locations are perceived and described for the given case study.These results are the input to section 4, where we describe the concept andprototypic implementation of a VGI system for environmental information (eVGI)for the given case study. This is followed by conclusion and future work items insection 5.

2. PREVIOUS WORK

In this section we describe previous work in the field of VGI initiatives and relatedsystems. We focus on of the aspect of vagueness of geographic information andhow to capture it, and on the use of gazetteers.

2.1 Volunteered Geographic Information

The World Wide Web recently experienced a major shift in terms of technologyand user paradigms. Technologies like web servicesat the server side (Cerami,2002), and AJAX at the client side (Sayar et al., 2006) enhanced interoperabilityof components and modularity of the platform, making any piece of informationubiquitous. At the same time, user-generated content gained a critical mass, sothat by now the content of blogs, wikis, and social networks is seen as thewisdom of the crowds (O'Reilly, 2005). This new version of the Web,characterized by user-generated contents, modularity and social networking, isoften referred to as Web 2.0.

According to Goodchild (2007), the term Volunteered Geographic Information(VGI) is used to designate any user-generated content that has a relation to thesurface of the earth. Popular examples are GPS tracks of cars and points ofinterest such as look-outs, restaurants, coffee bars, etc. There are various VGIapplications that allow users to upload and browse information in various media

(text, pictures, videos, documents, etc.). The information is linked through aspatial reference to a location on a map. In the following sections we describesome prominent initiatives and their online applications for uploading andbrowsing VGI.

OpenStreetMap2 is one of the most famous VGI initiatives. The OpenStreetMapproduct is a free, editable and general-purpose street map. It is created by

2http://www.openstreetmap.org/


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collaborative methods, where users can upload new streets through GPS tracksor modify existing information (e.g. for the purpose of quality enhancement). ThisVGI initiative aims to extend the geographic coverage of the OpenStreetMapproduct to the whole world. At time of writing, it contained more than 22 millionsof kilometres of roads, covering 114 countries on the 5 continents(OpenStreetMap, 2009).

The WikiMapia initiative3 was inspired by the success of the online multilingualencyclopaedia, Wikipedia. However, other than Wikipedia, WikiMapia focuses onproviding information strictly related to a particular geographic location (i.e. abouttowns, cities, lakes, regions, etc.). It offers a map interface to browse the content.Users can create bounding boxes, or more detailed polygons inside a bounding

box. They can insert in addition a title, a short description, and a link to aWikipedia page that gives more information about the described item. Users canalso specify which language they used.

Google Maps, the geographic interface to the Google search engine, allowsusers to create VGI in the form of all-purpose personal maps4. Such maps (calledMy Map) are collections of points, lines or polygons that are associated withmedia items (e.g. text, html documents, photos, videos). The contents of suchmaps can be searched by other users that selected the option search user-created contents.

These examples illustrate how VGI can concern vast amounts of data, and findapplications in various domains. In addition, VGI becomes always moreubiquitous, with, the possibility to geotag blog posts5 , or to generate geotaggedmessages and photos or videos directly from GPS-enabled smart phone.

2.2 Vagueness in geographic information

A concept is known as vague if at least one of its characteristics does not obey toBoolean logic. The sorties paradoxprovides a concrete illustration of vagueness(Fisher, 2000). If we try to answer to the question: How many grains of sand dowe need to have a heap of sand? we wont obviously be able to provide a clearnumeric answer. In logical terms, we cannot set a border value N, where If the

number of grains is > N then this.IsHeap is True else, this.IsHeap is False.Similarly, we cannot set a clear fixed N, the number of (kilo)meters between thepoint A and the point B where If distance between A and B < N then A is closeto B, else A is far to B. It would have no sense if a single meter drasticallychanges the spatial relation between A and B.

3http://wikimapia.org/

4http://maps.google.com/support/bin/answer.py?hl=en&answer=68480

5http://bloggerindraft.blogspot.com/2008/12/new-feature-geotagging.html


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Geographic information offers numerous examples of vagueness: What are theboundaries of downtown Santa Barbara? (Montello et al., 2003) How to delineateregions like Midlands or Rocky Mountains? (Arampatzis et al., 2006) What is theextent of a given meteorological phenomenon (e.g. a rainstorm)? Where is theborder between the rural area and the urban area in a region? What portion of ariver is polluted by a given pollution source? (Dilo et al., 2007) In all those cases,concrete concepts would be very difficult to delineate with precision on a map.

The type of VGI we are interested in are perceptions rather than measurements.VGI participants are not digital probes that are sending precise numeric valuesthrough a network of sensors. They are human beings interacting with a

computer (or any type of mobile electronic device) to share their perceptions(Goodchild, 2007). This is an important feature to take in account, because VGIparticipants perceptions about geography are vague by their own nature.Fishers (2000) works on perception-based geography led this author to thefollowing conclusions: [VGI participants] live in a world steeped in vaguenesswhere they function effectively, and they think about geography and space asvague concepts. [] Vagueness is a necessary part of the human experience ofgeography. [Therefore,] it is essential that geographical databases should usethe same vagueness in user interaction.

2.3 Modelling vagueness using degrees of truth

Geographic Information Systems are traditionally based on a crisp object modelthat does not fit with vagueness modelling (Burrough, 1992)(Cross & Firat,2000). This object model provides the ability to encapsulate any real-lifegeographical object as a unit of spatial and alpha-numerical (attribute)information along with methods that specify meaningful operations on thoseobjects. The information that characterizes an object is not vague: the spatialcomponent is a precise point, path or polygon, and attributes have a precisevalue (text, number or date in most cases). As an alternative to the object model,the raster data model is useful to describe continuous spatial variables.According to this model, numerical values are assigned to each pixel of a rasterdataset, which are portrayed using colour scales (Bastin et al., 1999). VGI

systems are usually based on the crisp object model to encode, store and portraydata.

The concept of degree of truth is useful to reconcile object model withvagueness. Underlying this concept, the multi-valued logic aims to replace aBoolean vision of objects characteristics. In other terms, we can express with thedegree of truththat an object tends to have a given characteristic to some extent(expressed in a continuous scale form 0 to 1) instead of being forced to say thatthis object has (1, true) this characteristic or not (0, false). Applied to the sorties


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paradox, we can say that A is close to B has a higher degree of truthwhen thedistance between A and B is 10 kilometres than when it is 1000 kilometres(Fisher, 2000). This concept is often used by spatial analysis techniques: a rasterdata set shows the spatial distribution of the values of the degree of truthof agiven parameter (Dilo et al., 2007).

Two techniques for modelling vagueness while using an object data model canbe derived from the concepts described in this section:

objects with specific attributes that express degrees of membership tomodel vagueness about their spatial and non-spatial characteristics canbe captured and stored in such systems;

raster layers can be used to portray information with vague geographicboundaries.

2.4 Gazetteers, geographical names and natural language

Gazetteers are directories of place names matched with geographic coordinates(ISO, 2003). A web service that is built on top of such a directory and integratedinto a web application allows users to query a place by typing its name, andautomatically zoom to the corresponding location (OGC, 2006). In other words,users can use the knowledge inside the gazetteer to translate their verbalknowledge (i.e. place names) in geographical information (i.e. locations displayedon a map). Prominent examples of online gazetteers are the open source

Geonames

6

, the Getty Thesaurus of Geographic Names

7

and the GEOnetNames8 Server created and maintained by the U.S. National Geospatial-Intelligence Agency.

Gazetteers are usually built on top of administrative data sets provided by publicmapping agencies. However in real-world applications, vernacular names whichdo not correspond to those official place names are often used to name places

(Wang, 2000). There is thus a need to enrich gazetteers with vernacularnames to ensure that users can use their natural language to find or describegeographical locations. Several authors contributed to develop this concept, suchas Jones et al. (2008), Goldberg (2007) and Goodchild & Hill (2006), but ageneric term to designate this particular case of gazetteers is still missing. In this

article, we will use the term open gazetteerto designate the concept of gazetteerenriched with vernacular place names.

Recent research proposed interesting strategies to obtain geographic referencefor vernacular names that are often used to describe regions with vague limits.

6http://www.geonames.org

7http://www.getty.edu/research/conducting_research/vocabularies/tgn/

8http://earth-info.nga.mil/gns/html/index.html


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Arampatzis et al. (2006), and then Jones et al. (2008), harvested information fromthe World Wide Web to find correspondence between vernacular names andofficial place names. On the basis of information retrieved through the Googlesearch engine, Jones et al. (2008) established relations between the Midlands(vernacular region name), and cities and towns (official place names) that werecited on web pages as part of this region. They could then give an approximateextent to Midlands and include it in their gazetteer. This approach, however, canbe expected to be less efficient if applied to place names that are used only by aparticular community, as it could be expected in the use case presented in thisarticle (see Section 3).

3. ANALYSIS OF STAKEHOLDER PERCEPTIONS

As we described in the introduction, the concepts for capturing perceptions andthe resulting vague geographic information is based on a real world case study.This case study was carried out by the Department of Social and EconomicGeography, Ume University. The study addresses sector-specific vulnerability toclimate change. The case study area is located in the European north, whereclimate change is expected to be particularly pronounced (cf. Anisimov et al.2007).

In this section 3 we will briefly describe the case study, its results and how itsresults were analyzed in relation to vagueness in geographic information. Westart of in section 3.1 with an overview over the case study area and the sectorsaddressed. This is followed in section 3.2 by a concise overview over the methodthat was used to collect stakeholder perceptions. We put a particular emphasison the geographic location. In section 3.3 we describe how the stakeholderperceptions were analyzed and which conclusions were drawn from it.

3.1 Case study area and sectors under consideration

This study focuses on multiple use of forest lands in Gllivare municipality,situated in far northern Sweden. The area includes forestry, substantialenvironmental protection, tourism with a focus on winter tourism, and reindeerhusbandry. Reindeer husbandry is in general practiced on the same area as

forestry, where forest owners ranging from industry to private small-holderforest owners hold an ownership right while reindeer husbandry holds a userright. Double land use systems thus operate in the same areas. In general inSweden, the numbers of stakeholders in these sectors vary considerably in thereindeer husbandry area, comprising some 40% of Sweden, there exist some2500 persons active in reindeer husbandry to some 40,000 private forest owners,with corresponding differences in importance for the GNP. In addition,environmental protection plays a large role in many inland and mountain-closemunicipalities, such as Gllivare, and is often seen as subtracting valuable land


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from forestry. This means that the interaction between forestry, reindeerhusbandry, winter tourism and environmental protection are crucial for land usepressure, which is increased by the effects of climate change. Northern Swedenalso has a well developed road network, which means that there exists afragmentation in terms of available land. Development and production orconservation pressures in the sectors are thus creating a situation that can beexpected to be further impacted by climate change. Climate change can here beexpected to impact the balance between sectors and strongly affect actors suchas reindeer husbandry that both requires large land areas and is highlyvulnerable to fluctuations across the freeze-thaw threshold (0C). Climate changecould also be beneficial to some larger actors, such as forestry, due to increasedforest growth, but impact e.g. local harvesting and transport conditions.

3.2 Collecting stakeholder perceptions

The volunteered geographic information has been retrieved from semi-structuredinterviews, approximately 1-1,5 hours long, undertaken during autumn 2008. Inthese interviews, the interviewees were asked to describe their land use, how thiswould be affected by specific projected climate change impacts (such as warmerwinters with more thawing events) and also to indicate important areas for landuse during different seasons on a map of the municipality. This means that thedata comprises both map-based volunteered information about important areas,and oral descriptions of the areas and land use. Often during interviews, interviewpersons also mention specific events (such as problems in moving reindeerthrough certain areas in relation to specific geographic information, for instance alocation or a river). Interview persons also describe differences in land use overtime, for instance, the different requirements they have during different seasons(e.g., migration routes or grazing land of different types). The interviews wererecorded and transcribed in full, which means that they were written out word-by-word in transcripts that are then possible to analyse for, for instance,geographical and seasonal use data. Interview selection was based on existingcompanies and administration in the sectors in the region, and constitutes a fullselection of actors within the sectors and selection parameters. Theseencompassed forestry and forest administration (main land owners Sveaskog aswell as separately their Model Forest representative, SCA, the Common Property

Board, the two Common Forests as well as the Swedish Forest Agencyadministration, the private forest owners interest group Norra Skogsgarna, andforest coordinator at the municipality), chairs of the five main reindeer husbandryunits having reindeer grazing in the area, the twelve existing winter tourism-focused companies, and the one existing environmental protection organizationas well as administration of environmental protection at the county administrativeboard. In total were interviews made with 28 persons.


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3.3 Interpretation of results

In order to understand how people in the case study perceive and describeenvironmental phenomena, we analysed the interviews undertaken in the casestudy area: From the transcribed interviews we extracted those expressionswhich the interviewees use that are related to location, hence called geo-quotes.To address the vagueness of environmental phenomena related to climatechange, we further narrowed down our search to those geo-quotes that describeenvironmental phenomena they observed and the resulting impact on theinterviewees. From the maps that were used during the interviews, we extractedthe way how stakeholders mark and delineate the geographic information thatsupported their geo-quotes. The following paragraphs briefly summaries thefindings that arose from the first round of qualitative data analysis andinterpretation.

Geo-quotes are located using reference points that are of importance for theparticular sector. Looking at the quotes we can distinguish those reference pointsthat describe elements which are artificial (e.g. man-made or conceptual) andthose reference points that describe the interviewees natural environment.Examples for such artificial reference points are: administrative units such asmunicipalities and settlements, the transport network including major roads andrailway lines, power lines, and power plants. Natural reference points are e.g.

particular vegetation-types, locations with vegetation that has certain qualities(e.g. the presence of tree lichen in forests) and topographic elements likemountains, rivers and lakes. Reference points might differ, depending on thesector they are used for. For example, reindeer herders repeatedly used theirpastures as reference points. The reference points are given in the language ofthe interviewee (e.g. Swedish or Smi).

The reference points do not necessarily mark the location itself where aperception was made, but they mark the point which is closest to theirobservation (e.g. east of ..., west of ). The stakeholders use furtherexpressions that mark a certain vagueness of their perceptions or their memoryof its exact location. Examples are up here, this mountain country here, or

here and there.

The interviewees marked locations of their perceptions on topographic maps.First screenings of the material reveal that they use points, lines and polygons, aswell as existing map features such as lakes and rivers to mark the location ofperceptions. The line features mainly delineated subsets of existing artificialreference points such as roads and power lines, in which cases they were asprecise as the map. Points and polygons on the other hand were used todelineate elements in the natural environment. Particularly the polygons can best


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be described as sketches: they do not mark a precisely delineated geometricobject, but a rather a rough estimation of the location.

4. VGI FOR ENVIRONOMENTAL DATA (EVGI) PROTOTYPE

The requirement of coupling web-based visualisation with functionality to addgeolocated user-generated contents is already addressed by numerous VGIclients. However, as Rinner et al., 2008 emphasised, the serious applications ofVGI are sparse. In addition, we did not find any that was addressing thevagueness that characterize the users perception of environmental phenomena.This is one of the main characteristics of the eVGI prototype we describe in detailin this section. The eVGI prototype uses the concept Degrees of Truth described

in Section 2 to encode, store and portray vague Volunteered GeographicalInformation.

In the following section we briefly describe the system vision and related usecases (section 4.1), followed by a description of the architecture (4.2) and themain system components (4.3 4.6).

4.1 System vision and use cases

Based on the results of the previous section, we develop a prototype for VGI forenvironmental data (eVGI). The system vision can be summarized as follows:The eVGI prototype shall be a web application. This application shall allow usersto encode and to visualise perceptions of environmental phenomena in form ofgeocoded testimonials. The focus lies on supporting the use of vernacular namesboth for browsing and creating testimonials, and to capture how vague the usersknowledge is concerning the exact location of the perception that underlies thetestimonial. The prototype is a proof of concept for the use of the followingapproaches:

open gazetteer: In order to allow users to describe locations using theirown words, the eVGI shall offer an open gazetteer that can be enrichedwith vernacular place names. As the given user community is rathersmall, we propose that users actively create new entries, rather than anautomatic harvesting mechanism (cf. section 2.4).

degree of truth: Assuming that the testimonials contain a certain degreeof vagueness, the eVGI shall offer a mechanism to capture (testimonialcreation) and to represent (testimonial visualisation) information on thedegree of truth concerning the location that a testimonial describes.

Based on the system vision and the suggested approaches, we identify three usecases when interacting with the system: (1) creating a new testimonial and (2)extending the open gazetteer with new vernacular place names:


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1. Create new testimonial: The user navigates to a point of reference in amap, supported by the open gazetteer, if necessary. He marks thelocation of his perception by drawing a point, line or polygon on the map.He evaluates for the given location the degree of vagueness. He adds histestimonial, i.e. a title and a body text that describes his perception at agiven place. The system visualises the testimonial, reflecting thelocations degree of truth.

2. Extend open gazetteer: In order to extend the gazetteer with a new entrythe user navigates to the place he wants to describe. He either draws apoint, a line or a polygon, or he uses the current bounding box to describethe extent of the place he wants to add to the open gazetteer. He thenadds a name to the place. In case that the open gazetteer already

includes the location, the user can extent the open gazetteer entry byadding a new vernacular name to an existing place.

4.2 Architectural overview

The eVGI prototype is based on a Service Oriented Architecture(SOA) to ensureinteroperability of the services, reusability of components, and extensibility of thesystem (Yang et al., 2007). The eVGI prototype implements OGC-compliant webservices (OGC, 2008), namely: OGC Transactional Web Feature Services (WFS-T) for user-created information encoding and OGC Web Map Services (WMS) formap rendering. The choice of OGC-compliant components has been motivatedby the fact that OGC standards are widely accepted in the GeographicInformation community. In addition, reliable Open Source OGC-compliantsoftware products are available and can be easily integrated as components intoour system. The figure 1 provides an overview of the eVGI architecture.

The eVGI prototype is based on a 3-tier architecture, where:

the presentation tier include the eVGI smart client (for encodinginformation) or any other OGC-compliant web map client (forvisualisation);

the logic tier is made of an OGC-compliant web server that allows us todeploy our eVGI web services;

the data tier is made of a GIS database (i.e. a database specifically

designed to store geographic objects and their attributes).

On the architectural point of view, eVGI prototype is quite classical. Its originalityresides in the way each component has been implemented. Each component isdescribed with more detail in the next sections.


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Figure 1: The architecture of the eVGI prototype.

4.3 Component #1: VGI data encoding (eVGI smart client)

The eVGI smart client offers user-friendly functionalities to encode environmentalVGI, taking in account its inherent vagueness. It is based on two JavaScriptlibraries: Openlayers9 (for mapping features) and ExtJS10 (for GUI layout andAJAX behaviours). It uses a Transactional Web Features Service (WFS-T) to

store Volunteered Geographic Information in the eVGI database. Using the eVGIsmart client, stakeholders can draw vector features (points, lines or polygons)and encode attributes as non-geographic information associated with eachfeature. It contains the testimonial itself, i.e. the perceptions they had on the fieldof environmental phenomenon they think to be related to climate change. Thoseattributes will also include important metadata about the geographic vagueness

9http://www.openlayers.org/

10http://extjs.com/products/extjs/


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that characterise a given testimonial. We included two types of vaguenessmetadata.

The first type is user-encoded vagueness metadata. This qualitative metadataprovides a self-assessment of VGI. When filling the attribute form, the userchooses in a dropdown list which level of geographic precision he considers histestimonial has. We propose the following list of values:

5 = its exactly there; 4 = its there;

3 = its more or less there;

2 = it must be somewhere around there;

1 = I m not sure if it is somewhere around there; 0 = I dont know where it is.

This approach has to be tested, in order to establish, in collaboration with thestakeholders, a list of values that contains both an appropriate number of valuesand an appropriate text associated with each of them.

The second type is system-created vagueness metadata. This qualitativemetadata provides us a more objective measurement of VGI vagueness. Inaddition to this self-evaluation of vagueness, the eVGI smart client automaticallystores the scale at which the feature as been drawn. Indeed, it has been provedthat encoding scale is a good indicator of geographic precision (Zhang &

Goodchild, 2000). For example, we expect that, if the user has a good idea thelocation of the place he refers to, he will zoom to a level of detail where he cansee lakes, rivers, land use and other topographic and artificial reference pointsthat will help him to locate the perception on the map. Oppositely, if the user hasonly a vague idea of the location, he most likely will not bother to zoom tooprecisely.

User-encoded and system-created metadata are very complementary and willprovide a good estimate of the vagueness that characterise every piece of VGIencoded trough the eVGI smart client.

4.4 Component #2: VGI data storage (eVGI Database)

The Figure 2 below shows the most important elements of the eVGI databasestructure: the Userstable and the Testimonialtable. The Users table stores theinformation required for user identification, such as unique identifier, nickname,and contact details. It furthermore stores system-specific user data, like its role inthe management of the eVGI system, his favourite language for the interface orthe field he is working in.


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The Testimonials table is the main table of the eVGI database: it stores theVolunteered Geographic Information itself. As in any classical GIS database,each record in this table contains a geographic feature (point, line or polygon,store in the Geometry field) together with alphanumeric fields called attributes.Among those attributes are the title and body text of the testimonial, as well asthe period of time it is referring to. The Testimonials table contains as well severalattributes that we can call Metadata about testimonials, as they are not part of thetestimonial, but they are telling us more about it. Three fields among thoseMetadata store the information about geographic vagueness of the testimonials:

scalecreatedstores the map scale at which the user had zoomed whenhe encoded the geographic component of his testimonial;

similarly, scalemodified stores the map scale at which the user hadzoomed when he modified the last time the geographic component of histestimonial, if applicable;

authorVaguenessAssesmt stores the value the user encoded to assessthe precision he encoded, on a scale from 5 to 0.

These Metadata about geographic vagueness of the testimonials will be usedwhen analysing the data, and to portray them, as described in section 4.6.

Figure 2: The eVGI database structure.

4.5 Component #3: VGI data portrayal (eVGI web services)

The portrayal of eVGI web services is based on the egg-yolk representationmodel (Cohn & Gotts, 1996). According to this model, each vague geospatialobject is represented by two elements: the yolk is a crisp geographic objectrepresenting the most certain part of the vague object, while the white is thebroad boundary that delineates limits on the range of vagueness. The degree oftruth decreases from 1 at the boundary between the yolk and the white to 0


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outside the white boundaries (Dilo et al., 2007). An example of suchrepresentation is provided in Figure 3.

Figure 3: The egg-yolk representation of vague point, line and polygon

As suggested by Bastin et al. (1999), we use a raster dataset to represent spatialuncertainty. We have thus to process our raw data (i.e. vector features withMetadata about spatial vagueness) in order to calculate all pixel values of suchraster data set. This pixel value will express a degree of truth for each vectorfeature, i.e. it will state how much likely a user-encoded object can beextrapolated to this pixel.

A mathematical function describing spatial distribution of vagueness still has tobe formalised. We see three main parameters for this function. The firstparameter is the distance to the encoded vector feature (D). It is inverselyproportional to the degree of truth as it decreases with distance, i.e. the furtherwe are from a vector feature, the less likely it can be extrapolated to our position.The second parameter is the scale at which the vector feature has been encoded(S, the scale denominator). It is proportional to the degree of truth if we assumethat, the bigger is the scale denominator, the smaller is precision of the vectorfeature and then the higher is the degree of trust. The third element is the user-encoded vagueness assessment (A, higher value mean means higher precision).It is inversely proportional to the degree of truth, as more precise information willhave a smaller degree of truth outside the vector feature. How these elements

should be combined into a function to determine the visualization still has to beestablished and verified in further research.

The portrayal of information contained in the eVGI is based on an OGC Web MapService (WMS). The legend is specifically designed to express the degree of truththat can be associated to the portrayed features. In the same time, the servicesupports GetFeatureInfo request, which means that any OGC compliant client


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can show to the user the contents of the testimonial associated with thosefeatures.

4.6 Component #4: Open Gazetteer for eVGI (eVGI open gazetteer)

The eVGI open gazetteer is based on a Web Feature Service, as recommendedby OGC (2006) best practices. Users can add entries to this gazetteer through aTransactional Web Feature Service (WFS-T).

Following the open gazetteer principle described in section 2.4, users can queryand enrich the eVGI open gazetteer using the eVGI smart client. It offers asearch placefunctionality with an interface made of simple text field for encoding

the name of the searched place, and a button to trigger the query. Depending onthe results, several cases can occur:

there is only one, not ambiguous result: the maps zooms automatically tothe corresponding location, and a message telling that the query wassuccessful is returned to the user;

there are several results: the list of results is displayed together withadditional information about (e.g. administrative subdivisions in which theplaces are situated) and the user is invited to select the one that fits to hisneeds (or to tell that none fits, see case #3);

there are no results, or the results returned dont correspond to the usersexpectations: in this case, the user is invited to enrich the gazetteer by

drawing the places bounding box and providing additional info (only theplace name is essential).

In consequence, the system will include vernacular names thanks to informationprovided by the users. They will be stored as new entries in a Gazetteer thatinitially will contain only official place names and those names will be added inthe gazetteer for further use. The eVGI Open Gazetteer will thus offer increasingpossibilities for the users to use their natural language to describe located events.The user will be able to visualise existing entries of the Gazetteer and to add anew place name to an existing feature if required.

5. CONCLUSION AND FUTURE WORK

In this paper, we presented the eVGI prototype, an innovative VolunteeredGeographic Information system. It was developed to address a real-world casestudy implying stakeholders from forestry, fishing and reindeer husbandry sectorsin the Barents region. We described the use cases, design, architecture andcomponents of the eVGI systems, with a particular focus on functionalities thataddress our research question: how can stakeholders the vague geographiccomponent of perception of environmental phenomena be integrated with the


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current vision of VGI?The eVGI prototype is a web-based system for encoding,storing and portray vague environmental information that can be hopefullyadapted to other projects involving environmental VGI.

The eVGI client we developed is graphical user interface (GUI) that allowscreating VGI together with Metadata about its geographical Vagueness. Startingfrom the observation on how stakeholders sketched paper maps, we madedesign assumptions to offer them similar functionality in digital form. Future workshould assess the functional quality of eVGI, by observing how stakeholders useit.

We justified the choice of the egg-yolk model (Cohn & Gotts, 1996), as it allows

to represent the user-encoded crisp object together with a spatial representationof its Metadata about vagueness. Portrayal of the vagueness information wecaptured should be improved by adaption a formal and well documentedmathematical formalism in this purpose.

Compared to information harvested on the World Wide Web (cfr. Jones et al.,2008)), the information encoded only by the users of the system is expectedconsiderably less vast, due to the limited amount of users. However, this form ofOpen Gazetteer is expected to be more adapted to sector-specific users that usetheir own address space.

We collected two types of VGI: gazetteer entries and testimonials. While for thetestimonials we captured vagueness of geographic information, this has not beenaddressed for the gazetteer entries. However, as Arampatzis et al. (2006)demonstrated, vernacular place names have also vague spatial extent. Thus,future versions of our prototype should take this fact in account. Anotherimportant research field for future works is the definition of ontology for opengazetteers. The implementation of adequate ontology would make possible theaddition of a hierarchy between place names (e.g. if a place is a part of a widerplace), the possibility to support multilingual entries, and the possibility to definethe thematic scope of entries (i.e. define to which sector of activity it belongs).

The eVGI is designed to collect perceptions from users of environmental

phenomena, taking in account potential vagueness of the geographic componentof such perceptions. Main current VGI systems, such as WikiMapia orOpenStreetMap, simply ignore this vagueness. Taking it in account is a steptowards quality assessment, and therefore towards credibility of VGI. Credibilityof VGI is an important field for future works. We should, for example, improve thequality control by implementing a peer-to-peer credibility assessment ( Flanagin &Metzger, 2008). This could be based on rating and commenting functionalitiesoffered to stakeholders.


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Finally, it is important to notice that this paper focused on the geographicalcomponent of the stakeholders perceptions. Future works should address thetemporal and thematic components as well.

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Addressing VGI Case Study