Synaesthesia is the blending of two senses, for example, where certain numbers “seem to be” certain colors. I don’t have that experience, but I do have a strong sense of the shapes of number lines and time sequences.
For example, the number line for me is not a straight line. It takes a left turn at 10, then a right at 20, then another right at about 80, and a left at 90. After 100, the 0-through-100 line repeats again, but for 200, 300, and so on, they line up like rows in a raster.
I was reminded of this because my local pool opened after a 10-week repair, and I had to print up a new weekly schedule for lap swims. To match my mental model of the week, I laid out the week like this:
This has the advantage of being intuitive (for me), and also fits nicely on a letter-size sheet of paper.
Other sequences have their own shapes: the months of the year, the years of the past two millenia, the hours in the day.
Most synaesthetic experiences seem to be about relating colors to words or letters. My wife strongly relates colors to months and sounds. This story mentions just my experience: shapes for time sequences.