Linetype

The linetype aesthetic defines the stroke pattern of lines: a succession of “on” and “off” parts of the line to make different stipple patterns. Linetype is most useful for line and path layers as a colorless way to differentiate between categories.

While linetypes are most useful for differentiating between discrete data, ggsql also comes with a sequential palette that gradually increases the amount of ink used for the pattern.

Literal values

Linetypes can be specified in two different ways. A couple of patterns are named and can be referred to as such:

Name	Stroke-dasharray	Description
`solid`	(none)	Continuous solid line
`dashed`	6 4	Standard dashed line
`dotted`	1 2	Dotted line
`dotdash`	1 2 6 2	Alternating dot and dash
`longdash`	10 4	Long dashes
`twodash`	6 2 2 2	Two different dash lengths

You can e.g. use these names when defining a manual palette for the scale:

SCALE linetype TO ['dashed', 'dotted', 'twodash']

You can alternatively specify a custom pattern using hex strings:

SCALE linetype TO ['44', '1343', '3c6c9c']

Each pair of hex digits represents on/off lengths:

'44' = 4 on, 4 off (50% ink, similar to dashed)
'1343' = 1 on, 3 off, 4 on, 3 off (dot-dash pattern)
'3c6c9c' = 3 on, 12 off, 6 on, 12 off, 9 on, 12 off

Valid hex patterns:

Must have 2, 4, 6, or 8 hex digits
Digits can be 1-9 or a-f (0 is not allowed)
Digits represent line lengths as multiples of the linewidth

Palettes

ggsql provides two linetype palettes which are generally enough for every need

The categorical palette is the default palette for discrete linetype scales. It consists of the 6 named patterns shown above in the same order. Since it is the only palette for discrete linetypes, there is rarely a need to specify it. The categorical palette is the default palette for discrete linetype scales. It consists of the 6 named patterns shown above in the same order. Since it is the only palette for discrete linetypes there is rarely a need to specify it.

Sequential palette

The sequential palette is the default for binned and ordinal linetype scales. It consists of up to 15 patterns with increasing amount of “on” and decreasing amount of “off”. This creates a visual progression from sparse (low ink) to solid (100% ink).

Example: 5-Level Sequential

Level	Ink Density	Description
1	~6%	Sparse dots
2	~29%	Short dashes
3	~52%	Medium dashes
4	~75%	Long dashes
5	100%	Solid

Accessibility

Linetypes work well for colorblind viewers
Combine with color for redundant encoding
Limit to 4-6 distinct linetypes for readability
Solid lines are most visible; use for primary data