Canvas and Readability
How canvas slots work, why your file declares its own size, and the column width the protocol reads as comfortable to read.
Pick a slot, ship your own size
Every template registers against a canvas slot. A slot is a name and an orientation - portrait or landscape - and that is all it is.
A slot does not set a size. Your file declares its own, in its width, height and
viewBox, and the protocol reads the size back off the file. Want 900 x 1400? Pick a portrait
slot and ship 900 x 1400.
The list of slots is fixed and the protocol owns it. You pick from it; you do not invent one. The names look like paper sizes, and they are not - treat them as labels with an orientation attached and nothing more.
A bigger canvas is not bigger type
This is the one that surprises people, so it is worth stating flatly.
Doubling your canvas changes nothing about how the finished piece reads. Every surface that displays your template scales the whole thing to fit its own width. A 700-wide file and a 1400-wide file with everything proportionally doubled render as the same picture at the same apparent size.
What matters is the size of your type relative to the canvas width. 18px type on a 700-wide canvas reads twice as large as 18px type on a 1400-wide one, because the second one is being shrunk twice as hard to fit the same screen.
So if the copy in your template reads too small, the fix is bigger type or a narrower canvas - never a bigger canvas.
The column
The protocol reads a body column as comfortable when a line holds roughly 45 to 75 characters.
Below 45 the eye returns too often and the text reads as a stutter. Above 75 the return gets hard to find and readers lose their place. This is a typographic rule about eyes rather than a Rising Tide invention, and it is the single most useful number to design against.
Characters per line depends on three things you control: the width of your content box, the size of your type, and the typeface. A wider column at the same size holds more; a heavier or wider face holds fewer. The starter template sets at about 68.
Two things the protocol does for you
It shrinks type to fit. If a writer sends more text than your box holds at the size you drew, the protocol scales the type down - and scales the line height with it, so the block keeps the proportions you designed rather than swimming in leading that never moved.
It checks your template before it goes live. The Asset Studio runs your file against the worst piece a writer could actually publish - the longest allowed text, in the word lengths that pack worst - and tells you what it found:
| What it says | What to change |
|---|---|
| column is too wide for this typeface | narrow the content box, or use a wider face |
| column is too narrow for this typeface | widen the content box |
| box is too short for this product | make the content box taller |
| canvas is too wide relative to its content box | narrow the canvas, or widen the box inside it |
Those verdicts are about the worst case, not the typical one. A template that passes them handles anything a writer can send it; one that does not will look fine most of the time and clip somebody's longest letter.
Short forms do not have this problem
A haiku cannot overflow a box drawn for a haiku. If your template uses numbered line slots rather than a content region, the column rules above do not apply to it - you placed every line yourself, and nothing is going to arrive that you did not size for.