A bit of background: London Lives (2010) is a digital edition of 18th-century London sources; at its core there are 240,000 manuscripts from several archives (parish, courts, hospital, guild). Explicit aim of the project was to switch research focus from institutions to individuals, emphasising 'plebeian' lives.
But this can have downsides: the Sessions Papers (City of London, Middlesex, Westminster + Old Bailey with very few petitions) are very large and varied bundles of documents (86,000 page images excl OB). London Lives leaves them oddly inaccessible; hard to get a real sense of the archive as a whole, or how to put what you find in context. So my much more long-term aspiration is to 'map' the Sessions Papers more generally.
Why start with petitions? They represent an identifiable, substantial subset of material within the archive; they're likely to be of interest to a range of researchers. Also personally, I don't know petitions quite as well as some other types of document, so I have new things to learn.
NB: You can navigate between slides using the arrows in the headers. The graphs are interactive: hover mouse/pointer over the body of the graphs to access more detailed information. ⇛ slide 1