Synesthesia is a neurological condition in which stimulation of one sensory or cognitive pathway leads to automatic, involuntary experiences in a second sensory or cognitive pathway. People who have this are called synesthetes.
This issue of Synth'Zine talks about Number-Form Synesthesia. A number form is essentially a mental map that consists of numbers. When a person with NumberForm Synesthesia thinks about numbers, a number map is involuntarily visualized.
I interpreted a 'mental map' of numbers as places and locations I associate with specific numbers and made collages and illustrations based on them.