I had no idea the spell worked this way!! It never gave me anything settle-able so I thought it was just a way to get a lumber yard near a settlement.

Every tile is influenced by its surrounding tiles. Each add bonuses to grain and materials (and essence sometimes), when you get enough bonus together (a total adding to I 6 or more) you should get a settable location. This is how the game decides how things work.

For essence you do need a shard, crystal crag, monument location. If they add an essence the chances are that you have reached the magic number 6 and has already shown on the map. But if such a place is living inside a swamp, then this would be a good place to get an essence location, but not likely to happen.

likewise you could turn the number to 8 and have "no bad cities". this is good for player and AI, and has made for interesting games, especially on larger maps.

It would also "force" use of this spell to have "more cities", making the spell better.