Why does a WildOgres ResourceType have a <Attribute>TileYieldEssence</Attribute> ?

Makes tiles around have extra yields.

By design according to Frogboy, ogres have extra essence around them, perhaps it is something in the lore.

Hmm interesting, not sure I quite get it though.  So the Wild_Mercenaries Resource has this entry:

<GameModifier>
   <ModType>Resource</ModType>
   <Attribute>TileYieldGrain</Attribute>
   <Value>1</Value>
   <PerTurn>1</PerTurn>
</GameModifier>

What does the Value signify here?  The Ogre resource has Value=9 (TileYieldEssence) and the Mercenaries one has Value=1 (TileYieldGrain).

I don't see anything on the map or elsewhere that indicates these tiles are yielding any actual essence/grain? 

Thanks.

I admit that after playing around with TileYields quite a bit, it's unclear to me what makes them show up on the map, and I can't say that they do or don't always work. For example, I attempted to make cliff/beach tiles have yields, and that didn't do a thing (visually, or on mouseover). And yes, I know that there is a setting you have to set in the environment section to make the yield go active...

Tileyields come from worldresources and terraintypes. They contribute to the bonuses a player sees when he is able to build a city in a particular location.

The yields you see on tiles in game are not the yields of that one tile, they are the cumulative yields of the surrounding tiles. It's sort of like CIV where a city uses multiple tiles around it, except simplified so you only have one number to look at. You are never going to see a yield number on a tile you can't build a city on, but the yields of the tiles surrounding it will be boosted by whatever amount.

OK thanks all that helps a lot, I didn't realize it worked that way.  A lot of this stuff is not particularly clear or documented (unless i've missed it somewhere - might check the manual again).

I've learnt more about how this game works from modding than playing!    

OK so as it turns out it does touch on this (briefly) in the manual.  Thought i'd post the paragraph here for completeness, underlined bits are my emphasis.