Is it true that people in early 19th century England always named their land and houses, as we see in Jane Austen's Pride and Prejudice, and why?
Yes, the people of English society took to naming their property, and the tradition dates all the way back to the 17th century. The country house, or manor, belonging to the landed gentry was actually a very substantial part of a village's economy. The country house operated a bit like its own government, much like a county operates today. The villagers lived and worked on the estate and the land owner earned income from the tenants' rent and crops. In addition, many of the county's important business and political events took place in the country home. Since the country home was as important to the British government as the English monarchy, names were established in order to mark important locations, much in the same way that cities, towns, villages, and counties are named.
The place names, however, were never arbitrary. Names were always chosen to "describe the people, the wildlife, or the countryside" surrounding that place (Rye, "Norfolk and Suffolk Place-Names"). One important country house in Pride and Prejudice is Longbourn, the Bennet's estate. We learn early on in the book after the Meryton ball that Longbourn is the name of both their manor house and their village in the line, "They returned therefore, in good spirits to Longbourn, the village where they lived, and of which they were the principal inhabitants" (Ch. 3). If the Bennets are the principle inhabitants it means that they are the land owners thereby owning the estate, which the village is named after. The word burna, borne, or bourn is an Old English name meaning brook or stream (Rye). Manor houses were also named after their owners (Moore, "What's in a name?"). Therefore, the name Longbourn most likely tells us that it is the home of who were most likely the Bennet's early ancestors, the Longs, and it is situated near a brook or stream.