Tile yields are only shown somewhere you can settle a city - i.e. not next to an existing city, if you can see a yield you can plop a city there, if not, you can't either because it's too close to another (actual distance is dictated by map size, you're allow cities closer together on smaller maps) or because it's barren.

Essence powers one city spell per point. It's true it could do with more to explain things, maybe list it alongside mana produced by a city, but you can see numbers on the governing screen, it should look like 0/0 showing active spells/essence. Also if you zoom in you can see active spells above the city with icons, or blank slots if you have the capacity for more.

I'd like the game to give you a prompt, it is easy to forget that there are free city enchantment slots going unused, especially for captured cities. Best way to check is just to go into the governing screen, have a look at the kingdom report and relations while you're at it. All useful stuff.

Hope that helps

To be  a little more clear, your need 6 tiles between your cites. Any tile yields on fertile ground will be hidden if they are within 6 tiles of a settlement. The numbers shown on each individual tile represent the sum of the tiles surrounding it.

When it comes to placement of your settlement:

1) you need to have a forest in one of the surrounding 9 tiles to build a logging camp,

2) and next to a river to build a pier.

You're welcome Rizzo, I agree it's come on leaps and bounds but there's always room for tweaking things. I'd like to be able to show unusable tile yields just to have a look to see if razing a city would free up a nice spot, but I can't see many other reasons to have a look. It's not really a problem when you get used to it.

Also to Glowing_Ember the actual distance between cities does vary by world size, it's in the xml somewhere... I remember spotting it but can't remember where offhand... I think it's only 6 tiles on medium and larger. Tiny it's either 4 or 5... IIRC.

Also, tile yield doesn't affect any building other than the city hub, there is the argument (I'm against) for snaking towards resources or other cities to expand your zone of control or for fast travel but you don't need to see tile yields for that. (It lowers the difficulty by manipulating mechanics that the AI doesn't use)

I've dropped in to watch the game development progress for what feels like forever and I enjoy reading through the ideas and seeing some of them come to life. It's a bit sad they can't all be done, but jack of all trades means master of none. I'm just glad essence is back in the game in some form. Miss dynasties, miss sov's having essence, oddly miss housing even though I didn't enjoy building it over and over... would love to see weather/LOS/tile properties other than movecost/global enchantments... but I suppose you have to understand that every feature has a cost and multiple effects

[Edit]

The city grain/material/essence is set on founding a city, it isn't in any way effected by expansion. That's why I said above that you don't need to have a look after settling.