Plot.sphere errors if not associated with a projection

[Fil]

Plot.sphere().plot()
> TypeError: n.sphere is not a function

it's all right, but we might want a better error message

[mbostock]

Yes, the crash is fine, but the error message could be improved.

[mbostock]

Probably the place to fix this is in d3-geo’s path by implementing the sphere method and throwing an error:

https://github.com/d3/d3-geo/blob/main/src/path/string.js

[Fil]

I've fixed it in dffc4b6 by ignoring Plot.sphere if not defined; we could add a warning there, or throw an error (or do nothing and delegate to d3-geo). (removed the fix)