Rare Spawn Overlay is no longer maintained. If you want a similar addon I would comment on this project https://www.curseforge.com/wow/addons/npcscan-overlay to try and get it updated for BFA. If someone wants to take up the reigns on this project I'll be happy add them as an author. That said, since that last few xpacs Blizzard's map API's have changed significantly so fixing this addon may be non trivial.

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Rare Spawn Overlay Places colored locations of areas on the map where certain rares can be found.

Shades the area of the Rare Spawns, in Outlands, Northrend, Cataclysm, and Pandaria zones.

Commands:

/rso [on/off/toggle]

This addon is best used in conjunction with http://www.curse.com/addons/wow/silver-dragon, i prefer this addon for scanning rares, cause you can set it to rescan every few minutes for rares with out needing to log and clear the cache folder. Works awesome on timeless isle, where rare respawn anywhere from 20 to an hour.

Known issue with Carbonite and ElvUI conflicting, will work on fixing it, if anyone might know a way, please send me a message, on the website or ingame @ Rapsheet (Malfurion-Horde)