My solution for this is going to be:
- Treat the map like video/media content
- Provide a text list similar to what's being displayed on the map on an alternate page. With the link clearly labeled as the accessible version.
- Provide a description of what the map is trying to achieve.
This is a section of the WCAG 2.0 that talks about linking to accessible versions:
http://www.w3.org/TR/2013/NOTE-WCAG20-TECHS-20130905/G73
Someone is trying to solve a similar problem here: