Editorial

Abstract

Introduction

Visualising Mobility
   Table 1

Visualising transitions

Visualising trajectories

Discussion

Conclusions

Acknowledgements

References

Case Studies Index

2. Visualising Geographical Mobility

The geographical movement of a single individual over their lifetime is one of the most easily visualised of all social processes, but it is a special case of a very complex class of time-based visualisation problems involving a single actor and a two dimensional space. Even here, there is a third dimension, time, which is not always easily represented. Demographic research has tended to concentrate on relatively infrequent movements by individuals which are classed as `migration moves', associated (hopefully) with changes of both employer and residence, but once we have the ability to trace individuals continuously much more complex patterns of movement emerge. Here we have a problem in that really detailed information about the activities of modern individuals may well be available, but they may object to it being displayed on the World-Wide Web! Let us take one well known figure from history, the late 19th century British politician William Gladstone. He left a daily diary (Matthews, 1986), and the entries for 16th-18th March 1880 look like this:

Figure 1: William Gladstone's Movements during the Second Midlothian Campaign, 1880

16. Tu.

[Dalmeny House, Edinburgh] Wrote to Mr Newton - Mr ... - Scotts. Saw Herbert G. & instructed him as Private Sec. Packing & off at 9.30. Was obliged to address the people at every point (5) before Edinburgh - At York there were I think 6000: very quiet. At Edinburgh the wonderful scene of Nov. was exactly renewed. Reached Dalmeny 8.30 PM. Read Tracts on Mr Cowan - Pr. Consort Vol V - Tourgenieff Terres Vierges. Evening with Mr Reid & Mr Richardson on the arrangements to be made.

17. Wed.

Wrote to Mr Madan - Mr Toynbee - Mr Murray - Messrs C. Scribner & Sons - Mr Adam l. & 2 Tel. Drove to Edinburgh. Great & most enthusiastic meeting in the Music Hall. Spoke 1hour: questions &c. followed. Worked up Probate Duty figures. Quiet evg at Dalmeny. Read England under Lord B. Began Pr. Consort Vol. V.

18. Thur.

Wrote to Mr Hinde Palmer - Rev. Mr Enraght - Lord Dalrymple - Herbert John G. - Mr MacCulloch - Mr Tennant MP - T. Reeves - J. Rankin - Mr Knowles Tel. - Mr Myers WE. Meeting at Corstorphine in Free Kirk. Sp. 1hour. And at Ratho in School: hour. All signs good. And dear dear Herbert is out for Middlesex. God be with him! Read Lefevre on Game Laws - Life of Prince Consort.

These days were the beginning of his second Midlothian campaign, the diary provides precise associations between dates and geographical locations, and the following map reconstructs his daily movements during the whole of the campaign (Figure 1). This map may look unremarkable, but note that this was part of a General Election campaign and Gladstone was effectively running for Prime Minister (see Southall, 1996). Can we imagine Tony Blair staying inside his own constituency in the same way? In a very simple way, the map makes a point that the diary does not, unless one is intimately familiar with the names of villages around Edinburgh.

Gladstone, of course, was a well-known politician whose movements were recorded not only in his diary, subsequently published, but by newspapers. The movements of `ordinary people', perhaps fortunately, are not systematically recorded in such detail, but there are many exceptions to this. One obvious exception is where researchers interview them, or ask them to keep a diary. In historical contexts, we can sometimes trace movements through autobiographies (see Southall 1996) or through the work of family historians. However, an unusual source which provides the basis for a number of examples used here are the records of an early trade union, the Steam Engine Makers' Society, which listed in their Annual Reports both their membership records, including transfers between branches, and details of all benefit payments to members, including a `traveling benefit' which assisted members as they traveled around the country seeking work.

Table 1 assembles together all the information on a whole series of the union's reports about a man called James Beardpark (although his name appears in a number of slightly different ways). They trace him moving from his first being listed in the Bolton branch in 1835 to his death in Derby in 1844. The list includes various payments of sick pay (he was off work for five months in 1838 due to an accident), his wife's funeral in 1837 and his own funeral in Derby, and in particular three periods when he was tramping around the country looking for work. In April 1840 he seems to have moved from Bolton to Leeds and joined the branch. In September 1841 he left Leeds, and tramped through several Lancashire towns but then we lose track of him for a time. He reappears in Stockton but left in April 1842, going first to London (probably partly by sea) and then through Southampton, Bristol and Birmingham until he ended up in Derby. The union paid funeral benefit on his behalf two years later, and more details were obtained from his death certificate. He died at the age of 35 `by the Visitation of God of Natural Causes'.

As with Gladstone, this career becomes a little clearer if we map it, as shown in figure 2. The blue dots are towns where he was listed as a member, while the red dots are towns where he received traveling benefit.

Figure 2: Movements of James Beardpark 1835-44

The problem with simple maps like those for Gladstone and Beardpark is that they do not provide an explicit time dimension, so this has to be added through annotations, and where a person visited the same location more than once the resulting map can be very confusing. Time geographers developed sophisticated graphical representations of the life course, such as the Figure 3, taken from Lenntop's chapter in Carlstein et al. (1978), but they have been used only rarely and at great cost in illustrators' time. The figure below represents the movements of a person over a single day. The three dimensions of geographical space have been collapsed into two in order to make room for a time axis. The movements of the individual in space and time are depicted in a continuous and indivisible path. In the example, the individual starts from the home and visits his [sic.] workplace, a bank, his work place and finally a post office, before returning home." The shaded bar at the right identifies periods spent traveling (in black) and at work (cross-hatched). This use of a pseudo-three dimensional representation suggests an obvious potential for computer graphics.

Figure 3: Example of an individual's path in a time-space coordinate system

These examples concern the movement of a single individual, but how can we best present the experience of a group? If we are limited to graphics that can be reproduced on paper, we begin to run short of dimensions: if one dimension is time and another is used to distinguish individuals, how can we show where they moved? These constraints lead naturally to our first lifeline diagram, where each career is shown by a single line or bar and event are indicated by symbols or changes in fill patterns along the bar. For example, the following diagram summarises the migratory history of a large group of members of the Steam Engine Makers' Society. The Figure 4 is a simple bit-map graphic, but it forms part of a far more complex example exploring the idea of `drill-down'.

To provide some background to this diagram, the late 1830s and early 1840s, the middle of the time-lines, were a period of severe recession (associated with Chartist unrest) and it would seem to have affected the north-west of England and towns such as Bolton particularly severely. As a result, many engineers were forced to look elsewhere. The members of this trade union were able to obtain financial assistance from other branches as they traveled around, and from this we have very precise records of their movement. Note that about half the membership worked outside Bolton at some time, and a significant fraction went abroad. Most men who moved did so more than once, and many ended up back in Bolton. In the working example, it is possible to click on some of the lifelines to obtain more information about individuals.

Figure 4: Subsequent Careers of 1835 Members of the SEM Bolton Branch

A second, very similar, example (Figure 5) of a lifeline diagram showing the geographical movements of twenty individuals is taken from Langton & Hoppe's (1990) work on rural-urban migration in mid-19th century Sweden

Figure 5: Life-time Migration histories of 20 people sampled from the husforhorslangder of Vadstena in 1855 (the numbers in the left-hand margin indicate occupations)

Figure 5 has been redrawn from the original figure, which covered 47 people and was limited to black and white. Rather than use colours, the original uses three weights of continuous line, three weights of dotted line and a wavy line to show the different `places of residence'. Arguably, so many different types of line confuse the reader and it would be better to provide less detail in the main diagram and more via `drill-down'. We have also taken the opportunity to make the point symbols more closely resemble those used in the previous example. Langton and Hoppe comment that the diagram:

"reveals much more fully the nature of the massive residential mobility shown in the tables. It was normal for people to change their place of residence at all stages of the life-cycle. Although there was a tendency for this mobility to be at its most frenetic when people were in their twenties, everyone had moved, some two or three times, by their early teens, and everyone continued to move about until their sixties and seventies if they lived so long".