Interesting concepts here. I think the first thing you need to know is the bounds for what is acceptable for the format. Are they 100% blind or visually impaired such that if big enough they could see enough to make it out. Also could they see enough so that you could color code it in some way. If 100% blind then whats the full set of options for a blind person on the end of the internet. I dont know if text to speech is the only one and what web interface is there for haptic devices ? I have never heard of one. Since sound is common and haptic is extremely rare then maybe a map covered with sound cues would be the best option. But you need to know what limits you have before you can decide how best to implement a map like that.