How much land is held in commonty.

There are no statistics available for the amount of land in Scotland held in commonty, however, it is likely to be a very small amount.
One of the difficulties with identifying such land is that the title deeds will not necessarily expressly convey a proprietary right of commonty. In past cases of doubt, the nature of the possession has been an important factor.
The Land Register is a modern, map-based register of title, managed and maintained by the Keeper of the Registers of Scotland. On first registration of an area of land in that register, the Keeper will examine the prior title deeds as well as other evidence submitted by, or on behalf of, the applicant for registration. If an applicant considered that their primary property carried with it a proprietary right of commonty in other land, they could include evidence to that effect in their application. The Keeper is not aware of any land held as commonty being registered in the Land Register.
Accordingly, the titles to any land that remains held as commonty are likely to be recorded in the General Register of Sasines. This register, which has been in operation since 1617, is a register of deeds and holds only the information set out in those deeds. Therefore, it is unlikely that land held as commonty could be identified from the Register of Sasines alone.
Parliament recently passed the Land Registration etc. (Scotland) Act 2012 that will ultimately allow for the completion of the Land Register, replacing the Register of Sasines. It will provide better, clearer information on ownership of all land in Scotland.