In 1855 Scotland was divided into 1028 registration districts based on the civil parishes. This number rose to 1082 in 1910 but the number has fallen significantly in the 21st century.
Registrars were appointed in each district to maintain the registers of births, deaths and marriages. Two copies of each register were kept, one being held locally and the duplicate being sent to the Registrar General for Scotland in Edinburgh.
Each registration district has a unique reference number.
Registration Districts of Scotland Guide
The Registration districts of Scotland guide (1.5 MB pdf) lists all districts in alphabetical order with the dates during which each was operative. It is based on the General Register Office for Scotland publication 'The registration districts of Scotland from 1855' known as the blue book. This version includes all changes up to January 2009 as well as the references and earliest dates for the Old Parish Registers from 1553 to 1854.
The blue book had appendices showing the registration districts for the cities. Scanned copies of the pages are made available here in portable document format (each file is less than 180Kb).