A line chart draws every series one pixel wide and solid. chls sets the width of the line in pixels, and turns a solid line into a dashed one.
chls takes one group of up to three numbers per series, in the order the series appear in chd, separated by |: chls=<thickness>,<dash_length>,<space_length>. Only the thickness is required.
The syntax is the one Google Image Charts used, so a chls value copied out of an old chart.googleapis.com URL renders the same line here.
A single number per series sets the width and leaves the line solid. Below, chls=1|4|8 draws the three series at one, four and eight pixels.
https://image-charts.com/chart?cht=lc&chd=a:10,14,12,18,22,20%7C30,34,32,38,42,40%7C50,54,52,58,62,60&chco=1F3B99,00A550,E8622A&chls=1%7C4%7C8&chs=700x280&chxt=x,y&chdl=chls%3D1%7Cchls%3D4%7Cchls%3D8&chdlp=b&chtt=Line+thickness
The second number turns the line into a dashed one, and the third sets the gap. chls=2,6,3 is a two pixel line drawn as six pixel dashes with three pixel gaps.
https://image-charts.com/chart?cht=lc&chd=a:10,14,12,18,22,20%7C30,34,32,38,42,40%7C50,54,52,58,62,60&chco=1F3B99,00A550,E8622A&chls=2%7C2,6,3%7C2,14,6&chs=700x280&chxt=x,y&chdl=solid%7C6+and+3%7C14+and+6&chdlp=b&chtt=Dash+patterns
Dashes are the usual way to mark a series the reader should read differently, a forecast or a threshold rather than a measurement. Keeping the dashed series the same width as the solid one keeps it legible without making it shout.
The three line chart types all accept chls, and they differ in what they draw around the line.
| cht value | What It Draws |
|---|---|
| lc | A line chart with points spaced evenly along the x-axis. Axis lines are drawn by default. |
| ls | The same chart with no axis lines, which is what a sparkline is. Useful when the chart sits inline in a table or an email. |
| lxy | A line chart where you give both coordinates of every point instead of the y values alone, as alternating x and y series. |
Appending :nda to any of them, as in cht=lc:nda, hides the axis lines even when chxt asked for them.
https://image-charts.com/chart?cht=lxy&chd=a:5,20,40,70,90%7C10,35,25,60,50&chls=3&chco=1F3B99&chs=700x260&chxt=x,y&chtt=cht%3Dlxy
chls covers width and dashes and nothing else. Line colours come from chco, and the shapes drawn at each data point come from chm.
The curve is not configurable. Image-Charts applies the same small rounding at every data point on every line chart, and no query parameter changes it, so a request for perfectly straight segments or for a heavily smoothed spline cannot be expressed in the URL. The reference documentation lists every parameter the API accepts.
