Geographical Citizen Science

The London Citizen Cyberscience Summit in early September was a stimulating event, which brought together a group of people with an interest in this area. A report from the event, with a very good description of the presentations, including a reflection piece, is available on the ‘Strange Attractor’ blog.

During the summit, I discussed the aspects of ‘Extreme’ Citizen Science, where we move from usual science to participatory research. The presentation was partly based on a paper that I wrote and that I presented during the workshop on the value of Volunteered Geographical Information in advancing science, which was run as part of the GIScience 2010 conference towards the middle of September. Details about the workshop are available on the workshop’s website including a set of interesting position papers.

The presentation below covers the topics that I discussed in both workshops. Here, I provide a brief synopsis for the presentation, as it is somewhat different from the paper.

In the talk, I started by highlighting that by using different terminologies we can notice different facets of the practice of crowd data collection (VGI within the GIScience community, crowdsourcing, participatory mapping …).

The first way in which we can understand this information is in the context of Web 2.0 applications. These applications can be non-spatial (such as Wikipedia or Twitter), or implicitly spatial (such as Flickr – you need to be in a location before you can capture a photograph), or explicitly spatial , in applications that are about collecting geographical information – for example OpenStreetMap. When looking at VGI from the perspective of Web 2.0 it’s possible to identify the specific reasons that it emerged and how other similar applications influence its structure and practices.

The second way to view this information is as part of geographical information produced by companies who need mapping information (such as Google or TomTom). In this case, you notice that it’s about reducing the costs of labour and the need for active or passive involvement of the person who carries out the mapping.

The third, and arguably new way to view VGI is as part of Citizen Science. These activities have been going for a long time in ornithology and in meteorology. However, there are new forms of Citizen Science that rely on ICT – such as movement-activated cameras (slide 11 on the left) that are left near animal trails and are operated by volunteers, or a network of accelerometers that form a global earthquake monitoring network. Not all Citizen Science is spatial, and there are very effective examples, especially in the area of Citizen Cyberscience. So in this framing of VGI we can pay special attention to the collection of scientific information. Importantly, as in the case of spatial application, some volunteers become experts, such as Hanny van Arkel who has discovered a type of galaxy in Galaxy Zoo.

Slides 16-17 show the distribution of crowdsourced images, and emphasise the spatial distribution of information near population centres and tourist attractions. Slides 19-25 show the analysis of the data that was collected by OpenStreetMap volunteers and highlight bias towards highly populated and affluent areas.

Citizen Science is not just about the data collections. There are also cultural problems regarding the trustworthiness of the data, but slides 28-30 show that the data is self-improving as more volunteers engage in the process (in this case, mapping in OpenStreetMap). On that basis, I do question the assumption about trustworthiness of volunteers and the need to change the way we think about projects. There are emerging examples of such Citizen Science where the engagement of participants is at a higher level. For example, noise mapping activities that a community near London City Airport carried out (slides 34-39) which shows that people can engage in science and are well placed when there are opportunities, such as the ash cloud in April 2010, to collect ‘background’ noise. This is not possible without the help of communities.
Finally, slides 40 and 41 demonstrate that it is possible to engage non-literate users in environmental data collection.

So in summary, a limitless Citizen Science is possible – we need to create the tool for it and understand how to run such projects, as well study them.

Completeness in volunteered geographical information – the evolution of OpenStreetMap coverage (2008-2009)

The Journal of Spatial Information Science (JOSIS) is a new open access journal in GIScience, edited by Matt Duckham, Jörg-Rüdiger Sack, and Michael Worboys. In addition, the journal adopted an open peer review process, so readers are invited to comment on a paper while it goes through the formal peer review process. So this seem to be the most natural outlet for a new paper that analyses the completeness of OpenStreetMap over 18 months – March 2008 to October 2009. The paper was written in collaboration with Claire Ellul.  The abstract of the paper provided below, and you are very welcome to comment on the paper on JOSIS forum that is dedicated to it, where you can also download it.

Abstract: The ability of lay people to collect and share geographical information has increased markedly over the past 5 years as results of the maturation of web and location technologies. This ability has led to a rapid growth in Volunteered Geographical Information (VGI) applications. One of the leading examples of this phenomenon is the OpenStreetMap project, which started in the summer of 2004 in London, England. This paper reports on the development of the project over the period March 2008 to October 2009 by focusing on the completeness of coverage in England. The methodology that is used to evaluate the completeness is comparison of the OpenStreetMap dataset to the Ordnance Survey dataset Meridian 2. The analysis evaluates the coverage in terms of physical coverage (how much area is covered), followed by estimation of the percentage of England population which is covered by completed OpenStreetMap data and finally by using the Index of Deprivation 2007 to gauge socio-economic aspects of OpenStreetMap activity. The analysis shows that within 5 years of project initiation, OpenStreetMap already covers 65% of the area of England, although when details such as street names are taken into consideration, the coverage is closer to 25%. Significantly, this 25% of England’s area covers 45% of its population. There is also a clear bias in data collection practices – more affluent areas and urban locations are better covered than deprived or rural locations. The implications of these outcomes to studies of volunteered geographical information are discussed towards the end of the paper.

“How good is VGI? A comparative study of OpenStreetMap and Ordnance Survey datasets” – published

The process of academic publication takes a long time, so only now my paper from 2008 is finally in print.

So the paper, which should be cited as:
“Haklay, M., 2010, How good is volunteered geographical information? A comparative study of OpenStreetMap and Ordnance Survey datasets” Environment and Planning B: Planning and Design 37(4) 682 – 703″

It’s abstract is:
Within the framework of Web 2.0 mapping applications, the most striking example of a geographical application is the OpenStreetMap (OSM) project. OSM aims to create a free digital map of the world and is implemented through the engagement of participants in a mode similar to software development in Open Source projects. The information is collected by many participants, collated on a central database, and distributed in multiple digital formats through the World Wide Web. This type of information was termed ‘Volunteered Geographical Information’ (VGI) by Goodchild, 2007. However, to date there has been no systematic analysis of the quality of VGI. This study aims to fill this gap by analysing OSM information. The examination focuses on analysis of its quality through a comparison with Ordnance Survey (OS) datasets. The analysis focuses on London and England, since OSM started in London in August 2004 and therefore the study of these geographies provides the best understanding of the achievements and difficulties of VGI. The analysis shows that OSM information can be fairly accurate: on average within about 6 m of the position recorded by the OS, and with approximately 80% overlap of motorway objects between the two datasets. In the space of four years, OSM has captured about 29% of the area of England, of which approximately 24% are digitised lines without a complete set of attributes. The paper concludes with a discussion of the implications of the findings to the study of VGI as well as suggesting future research directions.

The paper can be found here. If you are interest in a copy of the published version, email me.

The Tyranny of Place and OpenStreetMap

The slides below are from my presentation in State of the Map 2010 in Girona, Spain. While the conference is about OpenStreetMap, the presentation covers a range of spatially implicint and explicit crowdsourcing projects and also activities that we carried out in Mapping for Change, which all show that unlike other crowdsourcing activities, geography (and places) are both limiting and motivating contribution to them.

In many ways, OpenStreetMap is similar to other open source and open knowledge projects, such as Wikipedia. These similarities include the patterns of contribution and the importance of participation inequalities, in which a small group of participants contribute very significantly, while a very large group of occasional participants contribute only occasionally; the general demographic of participants, with strong representation from educated young males; or the temporal patterns of engagements, in which some participants go through a peak of activity and lose interest, while a small group joins and continues to invest its time and effort to help the progress of the project. These aspects have been identified by researchers who explored volunteering and leisure activities, and crowdsourcing as well as those who explored commons-based peer production networks (Benkler & Nissenbaum 2006).

However, OpenStreetMap is a project about geography, and deals with the shape of features and information about places on the face of the Earth. Thus, the emerging question is ‘what influence does geography have on OSM?’ Does geography make some fundamental changes to the basic principles of crowdsourcing, or should OSM be treated as ‘wikipedia for maps’?

In the presentation, which is based on my work, as well as the work of Vyron Antoniou and Nama Budhathoki, we argue that geography is playing a ‘tyrannical’ role in OSM and other projects that are based on crowdsourced geographical information and shapes the nature of the project beyond what is usually accepted.

The first influence of geography is on motivation. A survey of OSM participants shows that specific geographical knowledge, which a participant acquired at first hand, and the wish to use this knowledge and see it mapped well is an important factor in participation in the project. We found that participants are driven to mapping activities by their desire to represent the places they care about and fix the errors on the map. Both of these motives require local knowledge.

A second influence is on the accuracy and completeness of coverage, with places that are highly populated, and therefore have a larger pool of potential participants, showing better coverage than suburban areas of well-mapped cities. Furthermore, there is an ongoing discussion within the OSM community about the value of mapping without local knowledge and the impact of such action on the willingness of potential contributors to fix errors and contribute to the map.

A third, and somewhat surprising, influence is the impact of mapping places that the participants haven’t or can’t visit, such as Haiti after the earthquake or Baghdad in 2007. Despite the willingness of participants to join in and help in the data collection process, the details that can be captured without being on the ground are fairly limited, even when multiple sources such as Flickr images, Google Street View and paper maps are used. The details are limited to what was captured at a certain point in time and to the limitations of the sensing device, so the mapping is, by necessity, incomplete.

We will demonstrate these and other aspects of what we termed ‘the tyranny of place’ and its impact on what can be covered by OSM without much effort and which locations will not be covered without a concentrated effort that requires some planning.

OpenStreetMap completeness evaluation – March 2010

The opening of Ordnance Survey datasets at the beginning of April 2010 is bound to fundamentally change the way OpenStreetMap (OSM) information is produced in the UK. So just before this major change start to influence OpenStreetMap, it is worth evaluating what has been achieved so far without this data. It is also the time to update the completeness study, as the previous ones were conducted with data from March 2008 and March 2009.

Following the same method that was used in all the previous studies (which is described in details here), the latest version of Meridian 2 from OS OpenData was downloaded and used and compared to OSM data which was downloaded from GeoFabrik. The processing is now streamlined with MapBasic scripts, PostGIS scripts and final processing in Manifold GIS so it is possible to complete the analysis within 2 days. The colour scheme for the map is based on Cynthia Brewer and Mark Harrower‘s  ColorBrewer 2.

OSM Completeness 03/10

By the end of March 2010, OpenStreetMap coverage of England grown to 69.8% from 51.2% a year ago. When attribute information is taken into account, the coverage grown to 24.3% from 14.7% a year ago. The chart on the left shows how the coverage progressed over the past 2 years, using the 4 data points that were used for analysis – March 2008, March 2009, October 2009 and March 2010. Notice that in terms of capturing the geometry less than 5% are now significantly under mapped when compared to Meridian 2. Another interesting aspect is the decline in empty cells – that is grid cells that don’t have any feature in Meridian 2 but now have features from OSM appearing in them. So in terms of capturing road information for England, it seems like the goal of capturing the whole country with volunteer effort was within reach, even without the release of Ordnance Survey data.

On the other hand, when attributes are included in the analysis, the picture is very different.

OSM Completeness (with Attributes) 03/10

The progression of coverage is far from complete, and although the area that is empty of features that include street or road name in Meridian 2 is much larger, the progress of OSM mappers in completing the information is much slower. While the geometry coverage gone up by 18.6% over the past year, less than 10% (9.6% to be precise) were covered when attributes are taken into account. The reason for this is likely to be the need to carry a ground survey to find the street name without using other copyrighted sources.

The attribute area is the one that I would expect will show the benefits of Ordnance Survey data release to OSM mapping. Products such as StreetView and VectorMap District can be used to either copy the street name (StreetView) or write an algorithm that will copy the street name and other attributes from a vector data set – such as Meridian 2 or VectorMap District.

Of course, this is a failure of the ‘crowd’ in the sense that as this bit of information previously required an actual visit on the ground and it was a more challenging task than finding the people who are happy to volunteer their time to digitise maps.

As in the previous cases, there are local variations, and the geography of the coverage is interesting. The information includes 4 time points, so the most appropriate visualisation is one that allows for comparison and transition between maps. Below is a presentation (you can download it from SlideShare) that provides maps for the whole of England as well as 5 regional maps, roughly covering the South West, London, Birmingham and the Midlands, Manchester and Liverpool, and Newcastle upon Tyne and the North West.

If you want to create your own visualisation, of use the results of this study, you can download the results in a shapefile format from here.

For a very nice visualisation of Meridian 2 and OpenStreetMap data – see Ollie O’Brien SupraGeography blog .

Usability of VGI in Haiti earthquake response and the 2nd workshop on usability of geographic information

On the 23rd March 2010, UCL hosted the second workshop on usability of geographic information, organised by Jenny Harding (Ordnance Survey Research), Sarah Sharples (Nottingham), and myself. This workshop was extending the range of topics that we have covered in the first one, on which we have reported during the AGI conference last year. This time, we had about 20 participants and it was an excellent day, covering a wide range of topics – from a presentation by Martin Maguire (Loughborough) on the visualisation and communication of Climate Change data, to Johannes Schlüter (Münster) discussion on the use of XO computers with schoolchildren, to a talk by Richard Treves (Southampton) on the impact of Google Earth tours on learning. Especially interesting are the combination of sound and other senses in the work on Nick Bearman (UEA) and Paul Kelly (Queens University, Belfast).

Jenny’s introduction highlighted the different aspects of GI usability, from those that are specific to data to issues with application interfaces. The integration of data with software that creates the user experience in GIS was discussed throughout the day, and it is one of the reasons that the issue of the usability of the information itself is important in this field. The Ordnance Survey is currently running a project to explore how they can integrate usability into the design of their products – Michael Brown’s presentation discusses the development of a survey as part of this project. The integration of data and application was also central to Philip Robinson (GE Energy) presentation on the use of GI by utility field workers.

My presentation focused on some preliminary thoughts that are based on the analysis of OpenStreetMap  and Google Map communities response to the earthquake in Haiti at the beginning of 2010. The presentation discussed a set of issues that, if explored, will provide insights that are relevant beyond the specific case and that can illuminate issues that are relevant to daily production and use of geographic information. For example, the very basic metadata that was provided on portals such as GeoCommons and what users can do to evaluate fitness for use of a specific data set (See also Barbara Poore’s (USGS) discussion on the metadata crisis).

Interestingly, the day after giving this presentation I had a chance to discuss GI usability with Map Action volunteers who gave a presentation in GEO-10 . Their presentation filled in some gaps, but also reinforced the value of researching GI usability for emergency situations.

For a detailed description of the workshop and abstracts – see this site. All the presentations from the conference are available on SlideShare and my presentation is below.

Horizon’s ‘Supporting the contextual footprint – Infrastructure Challenges’ presentation

The Digital Economy is a research programme of Research Council UK, and as part of it the University of Nottingham is running the Horizon Digital Economy research centre. The institute organised a set of theme days, and the latest one focused on ‘supporting the contextual footprint – infrastructure challenges‘. The day was excellent, covering issues such as background on location issues with a review of location technology and a demonstration of car pooling application, data ownership, privacy and control over your information and finally crowdsourcing. I was asked to give a presentation with a bit of background on OpenStreetMap, discuss the motivation of contributors and mention the business models that are based on open geographical information.

For the purpose of this demonstration, I teamed with Nama Raj Budhathoki who is completing his PhD research at the University of Illinois, Urbana-Champaign under the supervision of Zorica Nedović-Budić (now at University College Dublin). His research focuses on user-generated geographical information, and just before Christmas he run a survey of OpenStreetMap contributors, and I was involved in the design of the questionnaire (as well as being lucky enough to be on Nama’s advisory committee).

So here is the presentation and we plan to give more comprehensive feedback on the survey during State of the Map 2010.

Haiti – further comparisons and the usability of geographic information in emergency situations

After the publication of the comparison of OpenStreetMap and Google Map Maker coverage of Haiti, Nicolas Chavent from the Humanitarian OpenStreetMap Team contacted me and turned my attention to the UN Stabilization Mission in Haiti’s (known as MINUSTAH) geographical dataset, which is seen as the core set for the post earthquake humanitarian effort, and therefore a comparison with this dataset might be helpful, too. The comparison of the two Volunteered Geographical Information (VGI) datasets of OpenStreetMap and Google Map Maker with this core dataset also exposed an aspect of the usability of geographical information in emergency situations that is worth commenting on.

For the purpose of the comparison, I downloaded two datasets from GeoCommons – the detailed maps of Port-au-Prince and the Haiti road network. Both are reported on GeoCommons as originating from MINUSTAH. I combined them together, and then carried out the comparison. As in the previous case, the comparison focused only on the length of the roads, with the hypothesis that, if there is a significant difference in the length of the road at a given grid square, it is likely that the longer dataset is more complete. The other comparisons between established and VGI datasets give ground to this hypothesis, although caution must be applied when the differences are small. The following maps show the differences between the MINUSTAH dataset and OpenStreetMap and MINUSTAH and Google Map Maker datasets. I have also reproduced the original map that compares OpenStreetMap and Map Maker for the purpose of comparison and consistency, as well as for cartographic quality.

OpenStreetMap and Google Map Maker - Haiti - 18 January 2010

MINUSTAH and OpenStreetMap - Haiti - 18 January 2010

MINUSTAH and Google Map Maker - Haiti - 18 January 2010

The maps show that MINUSTAH does provide fairly comprehensive coverage across Haiti (as expected) and that the volunteered efforts of OpenStreetMap and Map Maker provide further details in urban areas.  There are areas that are only covered by one of the datasets, so they all have value.
The final comparison uses the 3 datasets together, with the same criteria as in the previous map – the dataset with the longest length of roads is the one that is considered the most complete.

MINUSTAH, OpenStreetMap and Google Map Maker - Haiti - 18 January 2010

It is interesting to note the south/north divide between OpenStreetMap and Google Map Maker, with Google Map Maker providing more details in the north, and OpenStreetMap in the south (closer to the earthquake epicentre). When compared over the areas in which there is at least 100 metres of coverage of MINUSTAH, OpenStreetMap is, overall, 64.4% complete, while Map Maker is 41.2% complete. Map Maker is covering further 354 square kilometres which are not covered by MINUSTAH or OpenStreetMap, and OpneStreetMap is covering further 1044 square kilometres that are missing from the other datasets, so clearly there is a benefit in integrating them. The grid that includes the analysis of the integrated datasets in shapefile format is available here, in case that it is of any use or if you like to carry out further analysis and or visualise it.

While working on this comparison, it was interesting to explore the data fields in the MINUSTAH dataset, with some of them included to provide operational information, such as road condition, length of time that it takes to travel through it, etc. These are the hallmarks of practical and operational geographical information, with details that are relevant directly to the end-users in their daily tasks. The other two datasets have been standardised for universal coverage and delivery, and this is apparent in their internal data structure. Google Map Maker schema is closer to traditional geographical information products in field names and semantics, exposing the internal engineering of the system – for example, including a country code, which is clearly meaningless in a case where you are downloading one country! OpenStreetMap (as provided by either CloudMade or GeoFabrik) keeps with the simplicity mantra and is fairly basic. Yet, the scheme is the same in Haiti as in England or any other place. So just like Google, it takes a system view of the data and its delivery.

This means that, from an end-user perspective, while these VGI data sources were produced in a radically different way to traditional GI products, their delivery is similar to the way in which traditional products were delivered, burdening the user with the need to understand the semantics of the different fields before using the data.

In emergency situations, this is likely to present an additional hurdle for the use of any data, as it is not enough to provide the data for download through GeoCommons, GeoFabrik or Google – it is how it is going to be used that matters. Notice that the maps tell a story in which an end-user who wants to have full coverage of Haiti has to combine three datasets, so the semantic interpretation can be an issue for such a user.

So what should a user-centred design of GI for an emergency situation look like? The general answer is ‘find the core dataset that is used by the first responders, and adapt your data to this standard’. In the case of Haiti, I would suggest that the MINUSTAH dataset is a template for such a thing. It is more likely to find users of GI on the ground who are already exposed to the core dataset and familiar with it. The fields are relevant and operational and show that this is more ‘user-centred’ than the other two. Therefore, it would be beneficial for VGI providers who want to help in an emergency situation to ensure that their data comply to the local de facto standard, which is the dataset being used on the ground, and bring their schema to fit it.

Of course, this is what GI ontologies are for, to allow for semantic interoperability. The issue with them is that they add at least two steps – define the ontology and figure out the process to translate the dataset that you have acquired to the required format. Therefore, this is something that should be done by data providers, not by end-users when they are dealing with the real situation on the ground. They have more important things to do than to find a knowledge engineer that can understand semantic interoperability…

Haiti – how can VGI help? Comparison of OpenStreetMap and Google Map Maker

As the relief effort to the crisis in Haiti unfolds, so does response from mapping organisations with global reach. It is a positive development that free data is available from the Volunteered Geographic Information (VGI) community to assist humanitarian work on such a large scale, and good that there are now two sources. However, it is sad to discover that there seems to be friction between Google Map Maker and OpenStreetMap as to which organisation will prevail among governmental and NGO users. A key issue is surely to ascertain – and fast - which source of crowdsourced geographic information is most useful for which geographical area, and where the differences lie.

I did this assessment today, in the hope that it is useful for the emergency relief work now, and for the reconstruction work to follow. The data is current for the 18th January 2010, and the results are available  here.

The evaluation of the coverage of Google Map Maker and OpenStreetMap for Haiti was done using the same methodology as for the comparison of OpenStreetMap and Ordnance Survey data. The shapefile’s projection is UTM zone 18N. In the map here, yellow means that there is a better coverage in Map Maker, and blue means that there is a better coverage in OpenStreetMap. The difference between the two datasets is expressed in metres.

OSM and Map Maker coverage - Haiti - 18 January 2010

Unlike the previous comparison, where it was assumed that one dataset was the more accurate, here it is not helpful to pursue a binary approach. Rather, there are differences between the two sources of data, and these may matter as the relief work is carried out. The evaluation question is:  for each grid square, which of the datasets contains more information in terms of roads length?

The file contains the total roads length for both datasets. The calculated difference between them using the equation:

∑(OSM roads length)-∑(Map Maker roads length)

for each 1km grid square.

The information in the file can be used for the following applications:

• Users of these mapping products - it can help in judging which dataset to use for each area.
• Users – it can facilitate conflation -  the process of merging datasets to create a better quality output.
• Mappers - it can illuminate which areas to focus on, to improve coverage.

If you download the file, notice that the field OSMMMClose indicates that the two datasets are very close to one another – the value 1 is associated with grid squares where the difference between them is less than 200 metres. This might be useful as an indication that the two datasets agree with each other.

I hope that this assessment is helpful for those using the data for the relief effort. If you have ideas on how I can help further in this way, please get in touch.

OpenStreetMap and Meridian 2 – releasing the outputs

Back in September, during AGI Geocommunity ’09, I had a chat with Jo Cook about the barriers to the use of OpenStreetMap data by people who are not experts in the ways the data was created and don’t have the time and resources to evaluate the quality of the information. One of the difficulties is to decide if the coverage is complete (or close to complete) for a given area.

To help with this problem, I obtained permission from the Ordnance Survey research unit to release the results of my analysis, which compares OpenStreetMap coverage to the Ordnance Survey Meridian 2 dataset (see below about the licensing conundrum that the analysis produced as a by-product).

Before using the data, it is necessary to understnad how it was created. The methodology can be used for the comparison of completeness as well as the systematic analysis of other properties of two vector datasets. The methodology is based on the evaluation of two datasets A and B, where A is the reference dataset (Ordnance Survey Meridian 2 in this case) and B is the test dataset (OpenStreetMap), and a dataset C which includes the spatial units that will be used for the comparison (1km grid square across England).

The first step in the analysis is to decide on the spatial units that will be used in the comparison process (dataset C). This can be a reference grid with standard cell size, or some other meaningful geographical unit such as census enumeration units or administrative boundaries (see previous post, where lower level super output areas were used). There are advantages to the use of a regular grid, as this avoids problems that arise from the Modifiable Areal Unit Problem (MAUP) to some extent.

The two datasets (A and B) are then split along the boundaries of the geographical units, while preserving the attributes in each part of the object, to ensure that no information is lost. The splitting is necessary to support queries that address only objects that fall within each geographical unit.

The next step involves the creation of very small buffers around the geographical units. This is necessary because, due to computational errors in the algorithm that calculates the intersections and splits the objects and implementation of operators in the specific GIS package used, the co-ordinates where the object was split might be near, but not at, the boundary of the reference geographical unit. The buffers should be very small so as to ensure that only objects that should be calculated inside the unit’s area will be included in the analysis. In our case, the buffers are 25cm over grid square units that are 1km in length.

Finally, spatial queries can be carried out to evaluate the total length, area or any other property of dataset A that falls within each unit, and to compare these values to the results of the analysis of dataset B. The whole process is described in the image above.

The shape file provided here contains values from -4 to +4, and these values correspond to the difference between OpenStreetMap and Meridian 2. In each grid square, the following equation was calculated:

∑(OSM roads length)-∑(Meridian roads length)

If the value is negative, then the total length of Meridian objects is bigger than the length of OpenStreetMap objects. A value of -1, for example, means that ‘there are between 0 and 1000 metres more Meridian 2’ in this grid square whereas 1 means that ‘there are between 0 and 1000 metres more OpenStreetMap’. Importantly, 4 and -4 mean anything with a positive of negative difference of over 3000 metres. In general, the analysis shows that, if the difference is at levels 3 or 4, then you can consider OpenStreetMap as complete, while 1 and 2 will usually mean that some minor roads are likely to be missing. Also, -1 should be easy to complete. In areas where the values are -2 to -4, the OpenStreetMap community needs to do complete the map.

Finally, a licensing conundrum that shows the problems with both Ordnance Survey principles, which state that anything that is derived from its maps is Crown copyright and part of Ordnance Survey intellectual property, and with the use of the Creative Commons licence for OpenStreetMap data.

Look at the equation above. The left-hand side is indisputably derived from OpenStreetMap, so it is under the CC-By-SA licence. The right-hand side is indisputably derived from Ordnance Survey, so it is clearly Crown copyright. The equation, however, includes a lot of UCL’s work, and, most importantly, does not contain any geometrical object from either datasets – the grid was created afresh. Yet, without ‘deriving’ the total length from each dataset, it is impossible to compute the results that are presented here – but they are not derived by one or the other. So what is the status of the resulting dataset? It is, in my view, UCL copyright – but it is an interesting problem, and I might be wrong.

You can download the data from here – the file includes a metadata document.

If you use the dataset, please let me know what you have done with it.