The songs are listed in the index by accession number, rather than (for example) by subject matter or in order of importance.
Some well-known songs have low Roud numbers (for example, many of the Child Ballads), but others have high ones.
Some of the songs were also included in the collection Jacobite Reliques by Scottish poet and novelist James Hogg.
The index is a database of nearly 200,000 references to nearly 25,000 songs that have been collected from oral tradition in the English language from all over the world.
However, because of the practicalities of compiling the index (building on previously published sources) it is true as a general rule that older and better-known songs tend to occupy low numbers, while songs which are obscure have higher numbers.