Kohonen Self Organising Maps
Self Organising Maps (SOMs) can be used as 2d spatial summariser visualisations of multidimensional data. In the maps shown here, text distance metrics are generated from the weekly/monthly content on some of the more active mailing lists. Using a geographic like landscape metaphor, the height (colour gradient) indicates features with strong associations to all other features; proximity represents association between specific features (e.g. related terms), and label size indicates guide to basic frequency of a feature. There are many "correct" 2d map layouts for the same set of data (due to the multidimensional nature of the data), each map generation will usually settle into a slightly different set of local minima, but the associations are no less valid for each. After removing linguistic junk words, and word stemming, the maps currently pick the weeks/months top ~200 features by frequency. Each map is a continuous, tillable surface, and wraps around north/south and east/west (surface of a torus); so if you find an interesting label to one edge, remember to check it's neighbours on the opposite side.
What Do They Show?
Well, you could just treat them as tag clouds, showing the top two hundred word features used on the mail-list for a given week/month, but the maps also hold spacial information that provides context. Word features that appear close together on the map were used closely (on average) in email content from the mail-list. A height metaphor is used to indicate the combination of feature association strength and feature frequency; word features in the blue and green areas have weaker mean associations and frequency relative to the hot orange and pink highs, but should not be considered negatively as they are still in the top ~200 terms, and will often be tightly associated with surrounding neighbours.
SOM Related Research Papers
Self-Organizing Maps and Constructive Learning (PDF) Honkela T., Leinonen T., Lonka K., Raike A. (2000): Self-Organizing Maps and Constructive Learning. Proceedings of ICEUT'2000, International Conference on Educational Uses of Communication and Information Technologies, Beijing, China. August 21-25, 2000, pp. 339-343.
- In this article, the use of the self-organizing map (SOM) is approached on the basis of current theories of learning. Possibilities of computer and networked platforms that aim at helping human learning are also inspected. It is shown how the SOM can be considered a model of constructive learning. The area of constructive learning is outlined and two cases of using the self-organizing map in computer supported learning environments are presented.
It's An Education Project Mailing List
Sugar Mailing List
Technology in Education Academic Research Papers
A selection of SOMs for technology in education research papers relating to the One Laptop Per Child project can be found on the laptop.org wiki.
The mapping algorithms and visualisation style will continue to be refined, details will be posted on any significant modifications (see comments under images for changes). The code base was originally designed for bulk text documents from a single author, tested on works of literature from Project Gutenberg.