WORKSHOP REPORT

GIR’052005 ACM Workshop on Geographical Information Retrieval
Christopher B. Jones
Ross Purves
School of Computer Science Department of Geography
Cardiff University
University of Zurichc.b.jones@cs.cf.ac.uk
rsp@geo.unizh.ch

1

Introduction

Geographical information retrieval (GIR) is concerned with the problems of finding information
resources that relate to particular geographical locations. Until recently most web search engines havetreated geographical terminology within user queries in the same way as other terminology. This canoften result in failure to find relevant documents and in the retrieval of irrelevant documents. There
are several reasons for this. For example, there are many different places with the same name, so
unless the query contains a unique set of geographical terms, documents referring to the wrong place
may be retrieved. There are many uses of place names in the names of people and organisations withthe consequence that search depending on naive exact matching of terms may retrieve such
documents even though they may not relate to the named place. It is also the case that queries may
include spatial prepositions, such as near or outside, which will not be interpreted intelligently by thesearch engine. Thus relevant documents may not be found because the user’s query did not contain
explicit references to the places that match the query expression, in the sense of being, for example,
near, inside or north of a named place. It is also the case that conventional search engines lack otherdesirable facilities for geographical search such as relevance ranking that takes account ofgeographical proximity and the ability to use interactive maps to specify a query and to visualise theresults.
Limitations such as these in conventional search techniques have led to a growing body of researchconcerned with various aspects of geographical information retrieval. This includes topics such as
geo-parsing to detect geographical terminology in documents, geo-coding to attach an uniquelocational reference to a document, as well as the subjects of spatial indexing of documents,
geographical relevance ranking, user interfaces for geographical retrieval, retrieval of geo-data foruse in geographical information systems and issues concerned with the design and evaluation of GIRsystems,
The Workshop on Geographical Information Retrieval at CIKM’05 in Bremen, Germany inNovember 2005 was the successor to the very successful first GIR Workshop which was held inconjunction with SIGIR 2004 in Sheffield, UK. Both events attracted a mix of delegates withbackgrounds in information retrieval and in geographical information science. Details of theprogramme for GIR’05 can be found at http://www.geo.unizh.ch/~rsp/gir-cikm/. We now summarise
the content of the twelve presentations, following the order of the workshop programme.

ACM SIGIR Forum34

Vol. 40 No. 1 June 2006

2 Summary of presentations
The first three papers addressed the subject of visualisation in GIR. The paper by Carmo, Freitas,Afonso and Claudio described a method for modifying the amount of retrieved information that ispresented to a user in a way that adapts to the user’s expected interests. A degree of interest function
is based on attributes of the query topic and the distance of the displayed feature from the centre ofthe display. This is combined with multiple levels of detail of a map display. The approach isanalogous to the cartographic process of generalisation. In future work it is envisaged that the user
will be given control of specifying the attributes that determine the degree of interest.
Hobona, James and Fairburn reported on a multidimensional visual interface for GIR. They compareda 3-D graphics tool for visualising the results of information retrieval tasks with the approach of
conventional ranked lists, as used in a different geo-data search facility. They found that their 3D
visualisation method improved to some degree on the precision of results when compared with aranked list, while also being found to be superior with regard to several qualitative measures of easeof use. The study indicates that users are becoming more accepting of 3D visualisation methods thanhas previously been the case, possibly as a result of greater familiarity with computer games in which
3D graphics are commonplace.
The third of these papers, by Albertoni, Bertone and De Martino, addressed the problem of mismatch
between the user’s understanding of a subject area and the data content and vocabulary of a particular
set of resources that may be of interest. They proposed a query interface that allows the user tovisualise the data space in terms of specific categories of interest, individual values of which they
may select to refine their search. This is combined with visualisation of an ontology representing thevocabulary of the subject, enabling the user to consider using alternative data specific terms that areclose in meaning to their original query terms.
The identification of the geographical scope to which a web page refers is a major issue in GIR. Two
papers in the workshop addressed this task from differing, but complimentary, perspectives. The
work of Wang, Xie, Wang, Lu and Ma described three different forms of geographic location that canbe defined through the use of web pages and related data. These are the physical location of theprovider owning the web content, the content location - that is to say the place described by thecontent, and finally the serving location which is defined as the region within which the content is ofinterest. Both provider and content location are calculated through geoparsing of documents forreferences to geographic places found in gazetteers. A set of rules are used to distinguish between
locations which are likely to refer to provider or content location. Thus, for example, it is noted thatprovider location is likely to appear on multiple pages and be found more often in the header or thefooter of a page. Having identified possible candidates for provider location, a Support Vector
Machine is used to extract a probable provider location.
When specifying the content location of a web page, a key challenge lies in dealing with the fact thatmany web pages refer to multiple locations. Wang et al. describe an approach to identifying dominantlocations through the use of a weighted geographic tree based on the associations between thelocations grounded within the web page. Finally, serving location is calculated using a similaralgorithm, but using user locations (gleaned from server logs) and inbound hyperlink locations as
additional data sources. Initial results from the application of these algorithms to a relatively small
dataset show that, firstly, distinguishing between these different sorts of location is profitable since
76% of content locations are different from provider locations. Furthermore, for the test data used thealgorithms appear to give good results in terms of both precision and recall.
ACM SIGIR Forum

35Vol. 40 No. 1 June 2006

Clough’s paper is also concerned with the extraction of geographic location from web pages, though
in this case for a considerably larger dataset. Clough’s approach to the problem employs similar
geographic data sources, but focuses on correctly identifying geographic content, of any sort,contained within the web pages. He employs techniques from Named Entity Recognition to geoparsethe documents. Having grounded place names, Clough deals with the problem of referent ambiguity
by the use of default senses. Thus, he assumes that the mostly likely location referred to by aplacename is the one with the shortest administrative hierarchy (e.g. County -> Region -> Town).
The approach is simple enough to be applied to a range of different European countries, since therules applied are language independent. Clough reports on the performance of his approach for, onceagain, a relatively small sample data set. Finally, for four European countries, an analysis of theunique places identified in a collection of in excess of 800,000 web pages is presented, finding anaverage of around 3 geographic references per page.
Martins, Silva and Andrade reviewed different approaches to indexing and ranking in GIR as part of
the route to developing a spatially aware Portuguese geographic search engine. The paper sets outclassic text indexing methods before going on to examine the issues that must be considered whenretrieving information on the basis of not only context, but geographical scope. The nature ofsimilarity in terms of geographic scopes is examined, with relationships such as overlap, adjacency
and containment between scopes introduced. Such relationships also require that we develop
appropriate indexing and ranking methods, and Martins et al. list a number of possible spatial
indexing methods before discussing whether an index which combines geographic and contextual
scopes or separate indices is the best approach. Finally, they point out the importance of developing
an evaluation methodology for GIR, a point taken up in a subsequent paper presented at theworkshop.
The goal of the work by Desai, Knoblock, Chiang, Desai and Chen is to enable the retrieval of street
maps for a specified place from image and mapping resources on the web. As part of a process ofindexing the maps, methods have been developed to distinguish street maps from other types ofimage and then to categorise the street maps as either dense or sparse. Machine learning techniques
are used to detect images of street maps. Other pattern recognition techniques are used to detect road
network intersections, prior to employing map conflation methods to compare the map images with
vector data in order to derive the map coordinates and scales of the street images.
Much of the workshop dealt with the issue of retrieving unstructured data which contain somegeographic reference. However, there are large quantities of relatively structured spatial data (e.g.
remote sensing imagery, terrain models or maps of specific geographic attributes), containing explicit
georeferences, that are often generated as a consequence of research projects. Though such data often
have considerable potential for reuse, they are sadly underutilised due to their lack of accessibility.
Tschirner and Zipf described a portal based on open standards allowing such data to be exchanged
and, crucially, located. At the core of the portal lies the acquisition of standards-based metadata.
Through the use of a range of Open Geospatial Consortium standards these metadata can be queried
textually and graphically through a map interface before the datasets are uploaded by interested users.
Another problem associated with the use of structured geographical information is taken up in thepaper by Lutz. This is concerned with the problem of finding and composing geoprocessing serviceson the web in a manner that effectively matches the user’s requirements to web services that areavailable. The example that he gives is that of services to measure the distance between twolocations, given a service to provide the locations of airports. Issues to be addressed include the factthat there are different types of coordinate systems and different ways of measuring distance (e.g. inACM SIGIR Forum

36

Vol. 40 No. 1 June 2006

2D, 3D, on a plane or on a surface). Ontologies are used to provide a common vocabulary foradvertising and searching for service functions and associated data types along with pre-and postconditions (such as types of input and output coordinates) of the functions, represented in first orderlogic (FOL). The FOL aspect enables inexact matching between pre and post conditions using
subsumption (generalisation) relationships that may differ for the pre and post conditions. A
prototype of the “matchmaking process” has been implemented but further work is still to be done on
creating a web catalogue client to manage the process of registering and processing requests forservices.
The presentation by Exposto, Macedo, Pina, Alves and Rufino focused on the issue of crawling thecontent of the web itself. They postulate that distributing crawlers amongst geographic zones willlead to improvements in efficiency, and that geographical scope of web pages is likely to becorrelated with the geographic position of servers. They used a number of simple heuristics toattempt to assign zones to web servers, but found that only a few of these (the use of institution
names in host servers, and the NetGeo service) located a significant number of server IPs. Initial
evaluation of the results of distributed crawls based on geographically distributed partitioning showeddecreased download times with respect to both centralised and site-hash based partitioning. Theauthors suggest that by taking into account router locations and network topology, as well as theheuristics described in the paper, they may be able to improve the reliability of locations assigned to
web servers.
Delboni, Borges and Laender were concerned with automated interpretation of natural language
query expressions for purposes of geographical web search. They propose the use of textual query
expansion whereby a geographic query of the form <subject in-proximity-to landmark> istransformed to a disjunction of queries employing a variety of spatial relationships that refer toproximity, for example “near to”, “in front of”, “in the vicinity of “ etc. An experiment using theGoogle search engine showed that query expansion of this type improved both recall and precision
when compared with a single query phrase. Their intention is to enhance this form of query byattaching quantitative interpretations of the distance associated with the natural language expression
and hence introduce a spatial dimension to the associated relevance ranking.
The final presentation of the workshop by Martins, Silva and Chaves, considered the need forsystematic methods for evaluation of geographical information retrieval systems. The authors
distinguish between several aspects of GIR to which evaluation may be addressed, in particular thoseof finding geo-references within documents, assigning a main geographic context to a document(geographic scope), geographical relevance ranking, user interaction and computational performanceissues. The paper reviews some of the existing work on the various aspects of GIR evaluation andpresents some initial results from the authors on the recognition and grounding (geocoding) ofgeoreferences in text and of the assignment of geographical scopes to documents. The authors
highlight the difficulties in comparing the results of existing evaluation efforts, caused by the current
lack of a substantial standard document corpus that is marked up with respect to geographicalcontext.

ACM SIGIR Forum

37Vol. 40 No. 1 June 2006