Cobweb of flows - The Visualization of Spatial Social Structure - page 183

Many adults are not paid to work; in many areas these are the majority. Many
of those who do paid work do so within the ward in which they live. Thus even at
ward level commuter mapping is not representing the majority of people. Circles,
their areas in proportion to the number of people living and working in the same
ward, can give an indication of this phenomenon, while the flow lines between
wards are still shown.
At this resolution the direction of flow is implied from the context - where the
lines converge. Where lines cross it can be seen that the directions differ. There is
a problem when two major commuting flows overlap in completely the opposite
direction, but this is rare. The magnitude of flow is also difficult to see as the
lines all appear very thin. They are thin partly because almost all flows are small.
Colour can be used effectively to show how the structure of flow relates
to other social structures (Figures 6.15 and 6.16). The lines can be coloured
according to a particular feature of the areas: where people leave from to then
travel to work, about the work they do, where they are going, or even all three
aspects simultaneously.
Finally, it would be possible, though perhaps too confusing, to place the
flow map over a smoothed three-colour cartogram of some related aspects of
the population involved. If this were done with migration, the cartogram could
represent a few of the changes that the flows were producing.
The flows of travel to work are the heartbeats of the urban system, peo-
ple being pumped in and out of the cities. If they stopped there would be no
cities. The rhythm is well known, five days a week until Christmas. It may miss
a beat, but not often. Seeing the flows is fundamental to understanding them.
Understanding them shows us how society ticks.

6.6 Migration networks

The fact that among men aged under 50 the percentage of migrants
who were unemployed was greater for those moving within local
authority districts than for all migrants is difficult to reconcile with
the hypothesis of movement to find work. Although some districts
cover a large area, a more likely explanation for much of this
movement could be to find somewhere less expensive to live.
(Brant, 1984, p. 30)

What makes flow mapping in some other subjects simpler than within
human society is that most other flows are even more local, and mostly in one
direction - vector fields. Travel-to-work flows can be seen as an approximation
to this; most people go to work near to where they live and travel in the
same direction as other commuters. The extent to which this does not apply is
shown above. Internal migration (moving home) takes us much further from the
ideal, simpler, situation to visualize. Migration flows can be much longer, but