There are many websites that can be helpful for finding out about the Scottish Borders, whether you are planning to visit or not. Here are just a few of them (in no particular order):
A classic guide to the area is Andrew and John Lang's Highways and Byways in The Border, first published in 1913 and reprinted in later years. Most recently it was reissued in the United Kingdom by Senate in 1999, under the title Scottish Border Country, ISBN 1859585434 (439 pages). The book takes the form of a journey through the Border country and is full of local and historical snippets of information, as well as many pencil sketches of local places.
A more recent book which may be of interest is Charles Alexander Strang's Borders and Berwick: an illustrated architectural guide to the Scottish Borders and Tweed Valley. As the title suggests, it concentrates on the architecture of the area. However it is well illustrated with hundreds of photographs and contains short descriptions and historical notes on many places. It was first published in 1994 by the Rutland Press and its ISBN is 1873190107 (272-page paperback edition).
Chapter 9 of The Borders Book (see the Bibliography section) has a lot of information on the history of roads, bridges and railways in the Borders. More is given in Chapter 14, pp 171-176 as part of the chapter on the Industrial Revolution.
A 19th century county map of Peeblesshire is available online, although it is large (123 Kbytes) to download.