Impact factors of GIScience journals continue to increase in 2016

I am not a particular fan of the journal impact factor (IF): it is obsolete, it is susceptible to manipulation, and it does not guarantee quality. Furthermore, the distribution of citations within the same journal is usually highly skewed, which makes it inappropriate to talk about arithmetic means (on which IF is based). Even some editors of journals with a high IF denounce it openly.

Having said that, it’s hard to deny its importance in academia. For instance, in some countries it conditions promotions and the allocation of government funding.

For starters: the impact factor is a measure of citability of recently published papers in a journal. It is supposed to quantify the influence, reputation, and prestige of a journal; and everything is gauged and consolidated in a single number. The IF of a journal is calculated yearly as the number of references made to all papers published in the journal in the two preceding years, divided by their number (resulting in the yearly average of citedness of recent papers). For instance, the impact factor in 2015 of a journal is calculated as the ratio of cites in 2015 to papers published in 2013 and 2014, and the number of papers published in 2013 and 2014. For example, the journal Housing Theory & Society had published 42 papers in 2013 and 2014. In 2015 there were 43 cites to these 42 papers, as indexed by Thomson Reuters, resulting in an impact factor of 1.024. This also means that papers published before 2013 do not count. The same goes for papers published in 2015 (so a citation from a 2015 paper to a 2015 paper doesn’t count, nor ever will, oddly enough). Finally, not all journals have an IF – only those that are considered influential and of high quality by Thomson Reuters.

The IFs are announced yearly by Thomson Reuters in the Journal Citation Reports. The impact factors for 2015 have just been announced in the 2016 Journal Citation Reports. You can check them here if your institution has a subscription.

As I did last year, I checked the new IFs for the 19 journals that I consider relevant to people in GIScience. The list is composed from my scientometric paper published in IJGIS earlier this year (with the exception of JOSIS – Journal of Spatial Information Science, because it is not yet indexed by Thomson Reuters). For an extended list of journals please see the page compiled by my group.

The results are presented in the table below, also with the IFs in 2013 and 2014:


Generally the IFs continue to rise, as it was the case last year. On average, the IFs grew 16.5%.

The impact of 5 out of 18 journals has dropped: PFG‘s IF shrank by 24% (highest in relative terms), and IJDE’s by 0.5 (highest in absolute terms).

Cartography and Geographic Information Science is a clear winner, as its IF continues to grow substantially – from 0.5 to 2.2 in just two years.

While some journals experienced a considerable boost, in the previous edition their IF plummeted. See the case of GeoInformatica: 1.288 in 2013, down to 0.745 in 2014, and up by 42% to 1.061 in 2015. A substantial increase, but still lower than what it had two years ago.

One news is that the ISPRS International Journal of Geo-Information (IJGI), the Open Access journal published by MDPI got its IF (0.651) for the first time.

For some journals it paid off to deliberately delay paginating papers to boost the impact factor. There are some quintessential cases of holding papers without pagination for a long time, like Transactions in GIS:

2016-06-14 at 09.38

For IJDE that was not so lucrative: despite that the journal holds papers for long, its IF dropped. I wonder how much further it would drop if they didn’t employ such methods.

In total, the sum of all IFs continued to increase:


This might indicate that GIScience papers are recently attaining an increased reach outside the field. The results also show that IFs can be quite dynamic: IFs really go up and down, and in just one year their difference can be substantial, as for a third of journals (6/18) the IF changed by more than 30%.

Despite the general aversion to the IF, and its flaws, it’s certainly good news that GIScience papers continue to get more attention.

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Using 3D GIS to estimate population and refine census maps

The remote estimation of a region’s population has for decades been a key application of geographic information science in demography. Most studies have used 2D data (maps, satellite imagery) to estimate population avoiding field surveys and questionnaires. As the availability of semantic 3D city models is constantly increasing, in our new paper we investigate to what extent they can be used for the same purpose:

Biljecki, F., Arroyo Ohori, K., Ledoux, H., Peters, R., & Stoter, J. (2016). Population Estimation Using a 3D City Model: A Multi-Scale Country-Wide Study in the Netherlands. PLOS ONE, 11(6), e0156808. doi:10.1371/journal.pone.0156808

Based on the assumption that housing space is a proxy for the number of its residents, we use two methods to estimate the population with 3D city models in two directions: (1) disaggregation (areal interpolation) to estimate the population of small administrative entities (e.g. neighbourhoods) from that of larger ones (e.g. municipalities); and (2) a statistical modelling approach to estimate the population of large entities from a sample composed of their smaller ones (e.g. one acquired by a government register). Starting from a complete Dutch census dataset at the neighbourhood level and a 3D model of all 9.9 million buildings in the Netherlands, we compare the population estimates obtained by both methods with the actual population as reported in the census, and use it to evaluate the quality that can be achieved by estimations at different administrative levels. We also analyse how the volume-based estimation enabled by 3D city models fares in comparison to 2D methods using building footprints and floor areas, as well as how it is affected by different levels of semantic detail in a 3D city model. We conclude that 3D city models are useful for estimations of large areas (e.g. for a country), and that the 3D approach has clear advantages over the 2D approach.

The paper is Open Access.


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An improved LOD specification for 3D building models

The CityGML 2.0 LODs are an industry standard for conveying the grade of 3D city models. However, the 5 LODs are not defined precisely, and they are not sufficient for this purpose. In our new paper

Biljecki, F., Ledoux, H., & Stoter, J. (2016). An improved LOD specification for 3D building models. Computers, Environment and Urban Systems, 59, 25–37. doi:10.1016/j.compenvurbsys.2016.04.005

we present a refined series of 16 LODs that overcomes these issues:


The freely available author’s version PDF is available here. Please use the publisher’s version if available to you.

Abstract: The level of detail (LOD) concept of the OGC standard CityGML 2.0 is intended to differentiate multi-scale representations of semantic 3D city models. The concept is in practice principally used to indicate the geometric detail of a model, primarily of buildings. Despite the popularity and the general acceptance of this categorisation, we argue in this paper that from a geometric point of view the five LODs are insufficient and that their specification is ambiguous.

We solve these shortcomings with a better definition of LODs and their refinement. Hereby we present a refined set of 16 LODs focused on the grade of the exterior geometry of buildings, which provide a stricter specification and allow less modelling freedom. This series is a result of an exhaustive research into currently available 3D city models, production workflows, and capabilities of acquisition techniques. Our specification also includes two hybrid models that reflect common acquisition practices. The new LODs are in line with the LODs of CityGML 2.0, and are intended to supplement, rather than replace the geometric part of the current specification. While in our paper we focus on the geometric aspect of the models, our specification is compatible with different levels of semantic granularity. Furthermore, the improved LODs can be considered format-agnostic.

Among other benefits, the refined specification could be useful for companies for a better definition of their product portfolios, and for researchers to specify data requirements when presenting use cases of 3D city models. We support our refined LODs with experiments, proving their uniqueness by showing that each yields a different result in a 3D spatial operation.

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The variants of an LOD of a 3D building model and their influence on spatial analyses

The level of detail (LOD) concept conveys the grade of 3D city models, however, it still allows flexibility for different modelling choices. For instance, consider the following four (valid) variants of LOD1:



These variants, which we term geometric references, are a topic of our new paper which has been published in the ISPRS Journal of Photogrammetry and Remote Sensing:

Biljecki, F., Ledoux, H., Stoter, J., & Vosselman, G. (2016). The variants of an LOD of a 3D building model and their influence on spatial analyses. ISPRS Journal of Photogrammetry and Remote Sensing, 116, 42–54. doi:10.1016/j.isprsjprs.2016.03.003

The freely available author’s version PDF is available here. Please use the publisher’s version if available to you.


Abstract: The level of detail (LOD) of a 3D city model indicates the model’s grade and usability. However, there exist multiple valid variants of each LOD. As a consequence, the LOD concept is inconclusive as an instruction for the acquisition of 3D city models. For instance, the top surface of an LOD1 block model may be modelled at the eaves of a building or at its ridge height. Such variants, which we term geometric references, are often overlooked and are usually not documented in the metadata. Furthermore, the influence of a particular geometric reference on the performance of a spatial analysis is not known.

In response to this research gap, we investigate a variety of LOD1 and LOD2 geometric references that are commonly employed, and perform numerical experiments to investigate their relative difference when used as input for different spatial analyses. We consider three use cases (estimation of the area of the building envelope, building volume, and shadows cast by buildings), and compute the deviations in a Monte Carlo simulation.

The experiments, carried out with procedurally generated models, indicate that two 3D models representing the same building at the same LOD, but modelled according to different geometric references, may yield substantially different results when used in a spatial analysis. The outcome of our experiments also suggests that the geometric reference may have a bigger influence than the LOD, since an LOD1 with a specific geometric reference may yield a more accurate result than when using LOD2 models.

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Visiting the Singapore Land Authority

After participating at the GYSS 2016 I have spent several weeks as a visiting researcher at the Singapore Land Authority (SLA). SLA is now working on the 3D National Topographic Mapping Project, which involves the production of the island-wise 3D city model in CityGML in a very detailed LOD2 rich in thematic classes, attributes and texture. While ongoing, the project attracted great interest and it’s already a paragon of a national 3D city model. It was featured in media, it was already awarded, and a research programme was established to leverage its application.

During this visit I have also used the opportunity to visit several other institutions, such as the Singapore ETH Centre. More information about my stay is available at my group’s blog.

Thanks to SLA for the great hospitality.




Presentation at the Future Cities Lab @ Singapore-ETH Centre

Presentation at the Future Cities Lab @ Singapore-ETH Centre


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GYSS 2016 in Singapore

I’ve had the privilege of attending the Global Young Scientists Summit (GYSS) 2016 hosted by the Singapore University of Technology and Design (SUTD). GYSS is a one-week yearly multidisciplinary gathering of young scientists and researchers from all over the world, with eminent international science and technology leaders. The speakers are recipients of the Nobel Prize, Fields Medal, Millennium Technology Prize, Turing Award and IEEE Medal of Honour. So all very prominent, accomplished, and inspiring scientists. Besides attending lectures and plenary sessions, participants had the opportunity to visit different institutions, such as the Agency for Science, Technology and Research (A*STAR).

The event was kindly sponsored by the National Research Foundation of Singapore; and besides speakers there were other distinguished people, such as the President of Singapore with whom participants could have a chat (see photo below).

The event was well publicised in various media outlets.

All in all, a very cool event, from the opening to the closing ceremony. So if you are someone who is considering to apply for GYSS 2017 (or later), and you found this blog post by searching for more information on GYSS, my recommendation is do not hesitate: it’s worth a long travel 🙂

Here are some photos from the event, the campus of the university, and some landmarks of Singapore. My favourite one is with Dr Leslie Lamport, the recipient of the Turing Award, and the creator of LaTeX!

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and one with Dr Leslie Lamport…

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New paper in TGIS on the automatic update of road attributes by mining GPS tracks

I have co-authored a journal paper on mining GPS tracks for inferring road characteristics. Our method can be used to enrich road data sets, such as OpenStreetMap, to enhance its level of completeness.

van Winden, K., Biljecki, F., and van der Spek, S. (2016). Automatic Update of Road Attributes by Mining GPS Tracks. Transactions in GISdoi:10.1111/tgis.12186

Abstract: Despite advances in cartography, mapping is still a costly process which involves a substantial amount of manual work. This article presents a method for automatically deriving road attributes by analyzing and mining movement trajectories (e.g. GPS tracks). We have investigated the automatic extraction of eight road attributes: directionality, speed limit, number of lanes, access, average speed, congestion, importance, and geometric offset; and we have developed a supervised classification method (decision tree) to infer them. The extraction of most of these attributes has not been investigated previously. We have implemented our method in a software prototype and we automatically update the OpenStreetMap (OSM) dataset of the Netherlands, increasing its level of completeness. The validation of the classification shows variable levels of accuracy, e.g. whether a road is a one- or a two-way road is classified with an accuracy of 99%, and the accuracy for the speed limit is 69%. When taking into account speed limits that are one step away (e.g. 60 km/h instead of the classified 50 km/h) the classification increases to 95%, which might be acceptable in some use-cases. We mitigate this with a hierarchical code list of attributes.

The freely available author’s version PDF is available here. Please use the publisher’s version if available to you.


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A scientometric analysis of selected GIScience journals

Scientometrics and bibliometrics provide statistical techniques for measuring and analysing science. Scientometric studies have been carried out in many disciplines, but not particularly in GIScience. My study, published in IJGIS, bridges this gap.

Biljecki, F. (2016). A scientometric analysis of selected GIScience journals. International Journal of Geographical Information Science, vol. 30(7), July 2016, pp. 1302-1335. doi:10.1080/13658816.2015.1130831

Abstract: A set of 12,436 papers published in 20 GIScience journals in the period 2000–2014 were analysed to extract publication patterns and trends. This comprehensive scientometric study focuses on multiple aspects: output volume, citations, national output and efficiency (output adjusted with econometric indicators), collaboration, altmetrics (Altmetric score, Twitter mentions, and Mendeley bookmarking), authorship, and length. Examples of notable observations are that 5% countries account for 76% of global GIScience output; a paper published 15 years ago received a median of 12 citations; and the share of international collaborations in GIScience has more than tripled since 2000 (31% papers had authors from multiple countries in 2014, an increase from 10% in 2000).

The freely available author’s version PDF is available here. Please use the authoritative publisher’s publication if available to you.


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Applications of 3D City Models: State of the Art Review

My colleagues and I have published a new study in IJGI:

Biljecki, F., Stoter, J., Ledoux, H., Zlatanova, S., & Çöltekin, A. (2015). Applications of 3D City Models: State of the Art Review. ISPRS International Journal of Geo-Information, 4(4), 2842-2889. doi:10.3390/ijgi4042842

This review paper provides a comprehensive overview of use cases of 3D city models. During the work 29 use cases have been identified and described. The paper is supported by 400 references of related work. The PDF is freely available (Open Access) from the publisher’s website.



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UDMV 2015 held at TU Delft

After months of preparations, the Eurographics Workshop on Urban Data Modelling and Visualisation 2015 has finally been held on Monday 23 November. Previous editions of the workshop have been collocated with the Eurographics conference series, so we are happy that the first independent edition of the workshop has been hosted by us at TU Delft.

The workshop included the presentations of 11 peer-reviewed papers and 2 technical talks. Most authors and participants travelled from abroad, which shows that there is a substantial interest in this topic and that UDMV has a solid prospect of continuing as an independent event.

The papers were interesting, and the audience was mixed: from GIS to computer graphics, which warranted interesting discussions about common challenges and future collaborations. That was exactly the aim of the event.

Now back to writing papers 🙂



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