[bikacjgx] How to draw line graphs

How thick should one draw the line of a line graph?

A too thin line disappears when the image is scaled small, a too thick line is unclear where the data value is.

Solution, don't draw a line, instead make the region below the line a different color than the region above.

Inspired by how checkerboards may be drawn and scaled without choosing a line width, but Go boards 囲碁 do.