borders comprise one terrestrial border with England and sea borders,
two with England and several with other countries. The western sea
border with England extends seaward from the Solway Firth. The eastern
border extends into the North Sea from the mouth of the River Tweed.
The National Borders of Scotland
A paper by Dr James Wilkie and Edward Means (pdf
A Quick Look at Scotlands National Borders
A shorter version of the above document