OpenStreetMap Quality evalution and other comparisons
19 August, 2008
A comparison of my analysis of OpenStreetMap (OSM) quality evaluation to other examples of quality evaluation brings up some core issues about the nature of the new GeoWeb and the use of traditional sources. The examples that I’m referring to are from Etienne Cherdlu’s SOTM 2007 ‘OSM and the art of bicycle maintenance’, Dair Grant’s comparison of OSM to Google Maps and reality, Ed Johnson’s analysis this summer and Steven Feldman’s brief evaluation in Highgate.
The first observation is of the importance and abundance of well georeferenced, vector-derived public mapping sites, which make several of these comparisons possible (Chedlu, Dair and Feldman). The previous generation of stylised street maps is not readily available for a comparison. In addition to the availability, the ease with which they can be mashed-up is also a significant enabling factor. Without this comparable geographical information, the evaluation would be much more difficult.
Secondly, when a public mapping website was used, it was Google Maps. If Microsoft’s Virtual Earth had also been used, it would arguably allow a three-way comparison as the Microsoft site uses Navteq information, while Google uses TeleAtlas information. Using Ordnance Survey (OS) OpenSpace for comparison is also a natural candidate. Was this familiarity that led to the selection of Google Maps? Or is it because the method of comparison is visual inspection, so adding a third source makes it more difficult? Notice that Google has the cachet of being a correct depiction of reality, which Etienne, Dair and Bob Barr demonstrated not to be the case!
Thirdly, and most significantly, only when vector data was used – in our comparison and in parts of what Ed Johnson has done – a comprehensive analysis of large areas became possible. This shows the important aspect of the role of formats in the GeoWeb – raster is fabulous for the delivery of cartographic representations, but it is a vector that is suitable for analytical and computational analysis. Only OSM allows the user easy download of vector data – no other mass provider of public mapping does.
Finally, there is the issue of access to information, tools and knowledge. As a team that works at a leading research university (UCL), I and the people who worked with me got easy access to detailed vector datasets and the OS 1:10,000 raster. We also have at our disposal multiple GIS packages, so we can use whichever one performs the task with the least effort. The other comparisons had to rely on publically available datasets and software. In such unequal conditions, it is not surprising that I will argue that the comparison that we carried out is more robust and consistent. The issue that is coming up here is the balance between amateurs and experts, which is quite central to Web 2.0 in general. Should my analysis be more trusted than those of Dair’s or Etienne’s, both of whom who are very active in OSM? Does Steven’s familiarity with Highgate, which is greater than mine, make him more of an expert in that area than my consistent application of analysis?
I think that the answer is not clear cut; academic knowledge entails the consistent scrutiny of the data, and I do have the access and the training to conduct a very detailed geographical information quality assessment. In addition, my first job in 1988 was in geographical data collection and GIS development, so I also have professional knowledge in this area. Yet, local knowledge is just as valuable in a specific area and is much better than a mechanical, automatic evaluation. So what is happening is an exchange of knowledge, methods and experiences between the two sides in which both, I hope, can benefit.