Stroke styling for the optional river and road passes.
Optional
CSS color. Defaults: rivers #4d8ecb, roads #b39567.
#4d8ecb
#b39567
Stroke width in image pixels. Defaults to a fraction of scale (0.6 for rivers, 0.45 for roads), never thinner than 1px.
scale
Stroke styling for the optional river and road passes.