Using the width shape is a neat way to encode information

You can encode multiple dimensions or connect areas on a map

But you have to be careful!

We percive the thinest part of the line, not the height

Drag the circles to see how slope changes the width of the line

stroke-width works out of the box

But doesn't work with changing area, checkout d3-varible-width

Doesn't work for stacking

Since the height changes, lines won't add up to 100