This is a snippet I posted in a related question Children born overseas to British Subjects — what is their citizenship status?
I've seen other codes on the 1911 Census forms in red and green ink. What do the codes mean?
Via a search of ukbmd.org.uk which was suggested by @ColeValleyGirl for another question, I found these links on 1911census.co.uk :
The key for the occupation codes also has a link to the original occupation sheet on histpop.
The tally sheet for the birthplaces is image 10 of 14 in section in that set of images on histpop.
Does anyone know of other articles or links to more information about the office codes?