How do I add a historical map service?

[Nick-Hall]

@palos

Is there any easy way to add historical map service as linked below?

If the map service provides an open API then this should be possible. In the past we had a Stamen maps option, but this has been removed. Adding a new map may require a small amount of coding to re-enable some old functionality.

See also:

• Offer OpenHistoricalMap as an option for the map view
  Ideas
• Feature preview hack: Custom Map provider tiles