Line Interpolation Linear (default)

graph TB A --> B B --> C C --> D D --> A

Line Interpolation Basis

graph TB linkStyle default interpolate basis fill:none; A --> B B --> C C --> D D --> A

Line Interpolation Step-After

graph TB linkStyle default interpolate step-after fill:none; A --> B B --> C C --> D D --> A

Hierarchy Using Defaults

graph TB A --> B A --> C A --> D A --> E B --> B1 B --> B2

Hierarchy Using step-after

graph TB linkStyle default interpolate step-after fill:none; A --> B A --> C A --> D A --> E B --> B1 B --> B2

LR Hierarchy Using step-before

step-after works here too
graph LR linkStyle default interpolate step-before fill:none; A --> B A --> C A --> D A --> E B --> B1 B --> B2

Line Interpolation Cardinal

graph TB linkStyle default interpolate cardinal fill:none; A --> B A --> C A --> D D --> A

Line Interpolation Monotone

Monotone is monotonic in y, so it only looks good LR
graph LR linkStyle default interpolate monotone fill:none; A --> B B --> C C --> D D --> A

Mixing Line Interpolation Types

Specify the link number; the link must be defined first
graph TB A -- basis --> B A -- linear --> C C -- step-after --> D D -- cardinal --> A linkStyle 0 interpolate basis fill:none; linkStyle 1 interpolate linear fill:none; linkStyle 2 interpolate step-after fill:none; linkStyle 3 interpolate cardinal fill:none;