Prosopography is a new term: it does not appear in my edition of the Shorter Oxford English Dictionary reprinted and corrected in 1959. The Online OED gives this somewhat unhelpful definition:
a description of a person's appearance, personality, career, etc., or a collection of such descriptions.
[mass noun] the study of prosopographies, especially as an aspect of the study of Roman history.
Think of prosopography as a collective biography or, as a current prosopography practitioner has described it, "a means of profiling any group of recorded persons linked by any common factor". The prosopographical approach was used in the early to mid twentieth century by historians studying matters such as the governing class of imperial Rome, the creation of the American constitution and the motivation of members of the eighteenth century House of Commons.
According to Lawrence Stone, the populariser of the term prosopography, the approach was "Invented as a tool of political history, [but] it is now  being increasingly employed by the social historians." An outstanding example of such use was made soon after in Montaillou, the study of life, love and death in a C14 Pyrenean village, using a mass of depositions in the Vatican archives made by villagers to the Inquisition, determined to stamp out the last vestiges of the Cathar heresy in Occitania.
The advent of the computer and the development of database software that can easily be used by researchers has made the accumulation and analysis of socio-historical data much easier than any paper- or card-based system. A couple of recent examples, given on Wikipedia's Prosopography page, are Living and Dying in England 1100–1540 (a group picture of monastic life, centered on the aggregate experience of the monks of Westminster Abbey) and Angels in the Office (a group biography of women secretarial workers in the late 19th and early 20th centuries) . These give "a mosaic formed of documentary flashes of momentary insight into a multitude of obscure lives that can never be pieced together into individual biographies."
These researches focus on "Intentional Groups, with explicit shared interests", but there are more diffuse groups like that in A Preliminary Prosopography of the Victorian Street, in which "the spatial classifications, occupations, and domestic arrangements of a street in Victorian Oxford" were studied.
My projected prosopography of the Via Francigena would contain data on people who had travelled from England to Rome since the arrival of the mission of St Augustine in 597 up to, initially, the Norman Conquest in 1066. My first step will be to identify as many of these people as possible. I will identify them on two websites.
Oxford Dictionary of National Biography
Nearly all public libraries in the UK subscribe to the Oxford DNB online. This means I can access the dictionary, free, via my local library. On this index page I just type in BUCKS followed by my card number.
The Search facility enables me to search it for entries about people who lived between 597 and 1066 and where text in the entry contains the words "to Rome" or "at Rome". It is then a simple matter to copy the core information about the person (name, dates, office/rank) and the thirty or so words containing "to/at Rome". This raw list will later be used to tabulate the data.
Prosopography of Anglo-Saxon England
This extraordinary resource, developed over the last decade by Cambridge and UCL, is freely accessible without even having to log on here
I am searching the database via the left-hand frame by two of the seven search criteria:
Events > Life events/social and economic acts and relations > Journey (or Pilgrimage, if listed)
Location > Specific location > Rome
Each then lists individuals in the central frame, by name and identifying number: thus Alfred the cake-burner is shown as ALFRED 8: (m/l ix) the Great, king of the Anglo-Saxons, 871-899
Clicking on Alfred 8 displays in the right-hand column a Factoid (=incident with primary source reference) list. In Alfred's case factoids are grouped into 10 categories of which Events is one. This in turn has about 50 categories of which Journey lists 30 factoids, of which one reads
Æthelwulf 1.journey to Rome with Alfred 8: Æthelwulf 1 went to Rome with Alfred 8.: Asser.VitAlfredi 11 (855)
Clicking on the reference (Asser.VitAlfredi) displays details of both the edition of the primary source and its most recent translation.
Stevenson, William Henry – Asser's Life of King Alfred, Together with the Annals of Saint Neots Erroneously Ascribed to Asser. Edited with an Introduction and Commentary. – Oxford 1959 pp1-95
Keynes, Simon, and Lapidge, Michael – Alfred the Great: Asser's 'Life of King Alfred' and Other Contemporary Sources. Translated with an Introduction and Notes. – Harmondsworth 1983 pp67-110
These factoids will later be tabulated.
I do not yet know exactly how I will tabulate this data. I will decide this by the time the Winter Term starts on 18 January so that I can shortly after discuss with the Dean how I can use it when working on a new thesis as the final element of my MA course..