Yet another flow mapping post...

The reason for another of these posts is that I've been contacted by various people in different parts of the world (the USA, Australia, England) about flow mapping; how to do it, what to use it for and so on. Well, I think much more development is needed. I also need to keep blogging but I've been busy recently - poor excuse though. So, more results of my experiments in flow mapping... all of which use migration data from the 2001 UK Census.

First we have flow lines for the United Kingdom, at district level and then along the side I show different link magnitudes. This map shows 'gross' flows. That is, the flow lines represent the total link between two places (so, if A to B = 100 and B to A = 50, the gross link = 150).



On the second map, I've shown the same data but at ward level (n.b. there are about 430 districts and about 10,000 wards - as you'll understand, the migration matrices are pretty big). I've had to filter it to show only flows of 12 or more otherwise it's a jumbled mess.


On the third map, I've shown this data just for South East England, in the area surrounding London. This illustrates, to varying degrees of success, the level of functional polycentricity which exists in relation to household mobility.


Finally, I've attempted something different. I've produced a smooth surface raster, based on 2.5km cells, of all ward level migration. In some ways it is a success, but we can never really overcome all the limitations of 2D display. However, it does tell a story.

The New vs. the Old - Flow Mapping

Back again to a familiar topic - flow mapping. In the past all we had was paper and two dimensions. Now we have e-everything and things can easily be displayed in three dimensions (or 2.5D as we say in the GIS world). The reason for this post is that I'm currently revising some maps for a journal and I have come to the conclusion that some things just can't be effectively displayed in a static, old fashioned manner - they must be made interactive to work properly.

The map below shows about as much as it is possible to show in a traditional geovisualisation of migration. Here I have shown all moves into Manchester (the local authority) between 2000 and 2001, with reciprical links (i.e. where people have moved both in and out along the flow line path) in red, with unique inflows in yellow. I'm busy with other things now, and am still working a lot on the e-learning and screencasting side of things, so time to go...