The Map of Roman Britain produced by the Ordnance survey appears to show Britain at the time, but it really shows the Roman presence, omitting features of the local settlements.
The British landscape a the time of the Romans is generally seen as structured around elite estates centred on Roman style farms, or villae which controlled the surrounding farmland, but this is an image of Romans in Italy. when the Romans arrived, they arranged the land use in terms of need, but also in response to how the locals had behaved to them. Those who were co-operative were largely left to continue their lives, paying taxes for the priviledge, but where there had been heavy opposition, more land was taken out of their control.
Before, during and after the Roman period, far more people lived in the countryside than in the cities and towns. Current estimates suggest 200,000 people living in towns, 200,00 in military settlements, which includes civilians supporting them, and the rural population is estimated to be about 1.6 million.
So the Ordnance Survey, by recording all the Roman details – forts, villas, aqueducts, roads, milestones, mines, etc, have made some 80% of the population invisible.
This is further confused by the Roman allocation of tribes to certain areas, which were generally correspnded with Roman government areas; these tribal areas are about twice the size of modern counties, so claiming tribes covered much larger areas than in reality.
The Roman towns were largely populated by foreign traders, retired Roman soldiers and imperial administrators, so few locals lived there.
I was very surprised to read that Roman towns devoured people, ie even small towns were so filthy that towns were unable to maintain their own populations. I knew this wsa true in Georgian times, but this is incredibly early. But it makes sense.
It is generally assumed that when the Roman Empire fell, the towns followed into decline, but they were failing long before this; up to a century before the Romans left Britain, many towns were changing; in part this was due to the change from paganism to Christianity, with pagan sites of worship being destroyed or reused. But the overall sense is that Roman civilisation had never really taken root in Britain. At the borders of empire, it had required higher levels of military presence, so the cost on the locals had been higher, and the degree of integration lower. The high cost of garrisons also meant that there were fewer public buildings paid for by locals, so the social benefits of being romans was lower here than elsewhere in the empire.