Where is East Anglia?
The geographical area covered by this guide includes the English counties of Norfolk and Suffolk, as well as neighbouring parts of Essex, Cambridgeshire and Lincolnshire where the habitats are contiguous. Defining East Anglia's landward boundaries (to the south and west) has always been difficult, since cultural boundaries based on human colonisation, settlement and land use can differ widely from boundaries based on natural geography and geology. I've attempted to meld the two together to come up with a boundary based in part on geophysical features that can be followed on a map and in part on boundaries that more or less align with cultural boundaries.
Cultural East Anglia
A cultural identity to East Anglia can be traced back at least to the British Iron Age (from around 800 BCE to the Roman Invasion in 43 BCE), when the region became the domain of the Iceni people, a Celtic tribe with their capital at Caistor St. Edmund, near present-day Norwich. The Iceni occupied modern-day Norfolk, at least the northern half of Suffolk and neighbouring parts of The Fens that now fall into Cambridgeshire and Lincolnshire. Most famoulsy during the reign of the Iceni, their leader, Boudicca sacked the Roman regional capital of Colchester, forcing the Romans to decamp to London (which Boudicca also later laid waste to, along with St. Albans!).
With the decline of the Iceni after the fall of the Roman Empire, lands that had largely become unoccupied were invaded and settled by various peoples from the near-Continent, who came to be known collectively as the Angles. These people settled out into what became known as the 'North Folk' and 'South Folk', which in turn became 'Norfolk' and 'Suffolk', but they also populated a wider area to the south, east and north. Over time, cultural differences became less apparent, as regional wars and pacts redrew the maps and people began to travel and intermingle more widely; East Anglia became part of Mercia then Wessex for a time and all came under one ruler after the Norman Conquest. Since then, partitioning and appropriation of land has been due far more often to vested interests of individuals or, more latterly still, by regional and national politics than by anything cultural, so it remains to the distant past that we look for the clearest indications of a cultural East Anglia.
Yet still there remains clear, cultural signs of East Anglia, certainly in the place names, in the wealth of Saxon and early Norman, round-tower churches and in the great wealth of the buildings that still remain from the Middle Ages, when East Anglia became rich from the wool trade and Norwich was England's second city. The great draining of the wetlands of East Anglia began in the 1630s and saw an influx of workers from the Low Countries to help with the work. These people, along with Flemish settlers who brought a lace industry to Norwich, brought another cultural identity to East Anglia in the classic 'Dutch' style to the architecture, while this period also saw the introduction of the classic windpumps of the Norfolk Broads (so often wrongly called 'windmills'!).
Also by the 17th Century, Saffron Walden - politically in Essex - had established a trade in Saffron, growing large quantities of crocuses to be harvested for their stamens; this, to me, is very much an East Anglian identity and the town had much in common with East Anglia at that time, including in its architecture and in its puritan views. Later still, in the early 19th Century, came John Constable's classic paintings of Dedham Vale, an area so perfectly East Anglian, yet politically lying half in Essex and half in Suffolk. All of these local traits help in attempting to define some sort of boundary - no matter how vague - to a cultural East Anglia.
Geophysical East Anglia
In geophysical terms, the bulk of what we consider to be East Anglia is easily outlined by the North and East-facing coastlines of Norfolk and Suffolk, bulging outwards in a graceful arc into the North Sea. But defining the southern and western boundaries is far less straightforward. While the River Stour has long been used as the political boundary between Suffolk and Essex and is clearly a well-marked geophysical boundary, the coast to the south of its estuary has much in common with East Anglia, as does the city of Colchester. In addition, the culturally-defined Dedham Vale and town of Saffron Walden - as detailed above - need to be taken into consideration.
Since we are looking for a physical boundary that can easily be traced, on the Essex coast, I've considered the Blackwater Estuary to give a reasonably sound, southern edge to East Anglia, both geographically (south of there clearly becomes the Thames Estuary) and culturally. Having followed the Blackwater Estuary inland to Maldon, I've continued to use the River Blackwater as a useful, physical boundary. further upstream, the Blackwater becomes the River Pant and these rivers form a boundary that puts, for example, Coggeshall into our region, but Braintree outside, then continues northwest towards Saffron Walden. taking a line from the headwater of the Pant, around the south side of Saffron Walden, we meet up with the Fulfen Slade, a watercourse that runs into the River Cam. I should add that it would probably be more useful to actually use the southern boundary of the River Colne catchment as the southern edge of the region, but this would be hard to trace on a typical map and doesn't offer a physical boundary that can be seen out in the field.
So the River Cam makes a very convenient boundary to take us northwards to Cambridge and beyond, where the Cam confluences with the Great Ouse. As this would split Cambridge, I have allowed a bulge in the boundary to include the city itself for convenience. For the rest of the boundary, the low-lying region of the Fens forms an obvious boundary, though a precise line is difficult to define. From the confluence with the Great Ouse, we can follow that river westward to just east of Earith and from there, we can conveniently follow the western boundary of the vice-county of Cambridgeshire to the east of (and excluding) Peterborough. From here, political boundaries serve little purpose as they don't follow any geophysical boundaries. So it makes sense to attempt to include the bulk of the Fenland habitat and avoid any rising ground to the west or north, effectively following the 5m above sea level contour line. As a rough guide, this would give us a line that would pass between Peterborough and Whittlesey, between Market Deeping and Spalding, follow the South Forty Foot Drain north to Boston then head north-east along the railway line from Boston to the Sheeping River and follow the river through Wainfleet All Saints to the coast at Gibraltar Point, south of Skegness. This therefore includes the bulk of the Lincolnshire districts of South Holland and Boston, and a small section of East Lindsey.
By coincidence, my definition of East Anglia comes remarkably close to the political map drawn up in the late 1960s by Redcliff-Maud as part of a national government review of English regional boundaries, but which never got put into place.