One of the best things about working in an archive is that you are constantly learning and finding out about new sources of information.Like this website: http://www.nls.uk/maps/.
Although I have used the National Library of Scotland's website before, I had not used this feature. The selection of historical maps there is excellent.
Although not related, here is an interesting map. It is a plan of the Orkney Islands published by John Thomson and Co., Edinburgh showing the boundaries of the Earldom and the Bishopric (reference number D7/1/1).