Advance is a scheme where voters can vote up to 2 weeks (generally) before the election. In all these schemes a signature will be required before advance voting.
Signature is a scheme where all voters (not just advance voters) will be required to provide a signature before voting.
Scanning means that votes will be counted by electronic scanning machines. Y denotes a scheme using “commerically available” scanning hardware. X presumably denotes a scheme using scanning hardware custom-built by the Mayor’s nephew in his shed.
Internet denotes a scheme of advance voting using the internet.
Telephone denotes a scheme of advance voting using the telephone.
Central denotes the provision of a centrally provided facility (or facilities) at which voters can vote regardless of their ward or parish.