The reason for expanding my system was to cope with the one-hour marathon disciplines at memory championships. If you’re memorising a thousand-digit number with a simple two-digit-image system, each image will show up on average five times. It’s even worse with cards - if you’re using one card to an image and trying to memorise ten packs of cards, each image will appear ten times. Which is just way too confusing.
Most people got around that with a person-action-object system or similar, which reduces the repetition, but I wanted to stick with the simplicity of just having one image for each combination, and the freedom to associate them together however I wanted. So the only option was to go for a system with a whole lot of images in it.
As for creating the images, mostly it was just the first one I thought of. As I recall, I drew up a blank list of all the combinations, and filled in the first word that came to mind. At first I left a lot of blanks, but then when I had a three-day weekend to spare I forced myself to sit down and go through the whole list, writing down a word for each blank space. I never really thought about scientifically coming up with the most memorable image, or even about making sure no two images are too similar.
My ‘ideal’ training schedule (which I’ve never really stuck to since 2004, but which I still think of as the kind of thing I would do if only I could be bothered) was to do an hour of speed cards/numbers on weekday evenings after work, and then over the weekend do hour numbers, hour cards and 30-minute binary. Back in the olden days, very few people ever trained at the marathons, but I’ve always said it’s essential - it gets your mind accustomed to concentrating on one thing for long periods of time.
I’ve got 62 journeys that I use at the moment - each has 26 locations, for the simple reason that when I first started out, it took 26 locations to memorise a pack of cards. Nowadays I fit three packs on one journey, or the awkward number of 234 digits, or 780 binary (so one page and one line of the next).