The Sectional Appendix contains detailed information about each segment/sequence of the railway including speed, loading gauge and vehicle restrictions. Each LOR can be split into several pages and in this case 'seq' represents the specific page the information was taken from.
Line of Route (LOR)
Lines of route refer to strategic rail routes, and can be made up of several ELRs. For example, SBJ is the ELR for the line between Swanley and Ashford B junction. At Otford junction, the line diverges to Sevenoaks with an ELR of OJS. The line of route which covers Swanley to Sevenoaks is SO140. The LOR reference for any UK location can be found in the page heading of the Sectional Appendix line diagrams.
An Engineer's Line Reference (or ELR for short) is a three or four-character code used in the British rail network to refer to a section of a track or route. These references are unique across the whole rail network, allowing identification of any part of the network. Occasionally ELRs are used to refer to other railway infrastructure such as depots .