Im confused, GP improvements dont improve a resource?

For example building a mine on salt will give +1 food and +1 production.

Building any GP improvement will connect the salt to your trade network but will NOT give you the +1 food and +1 production....why?

Actually, GP tile improvements do not connect luxuries (like salt), but will connect strategic resources (horses, iron, etc). However, connecting a resource with a GP tile improvement does not give you the benefits of a standard tile improvement for that resource (e.g. For horses, it does not provide the benefits of a pasture, for iron it does not mimic a mine). Instead you get the unimproved yield of that tile plus the GP tile improvement yield.

Right, the only reason it connects strategic resources at all is to prevent frustration, as you might build a GP tile improvement only to discover later on that that tile is your only source of iron, or whatever, leaving you with the option either to live without iron, or remove your valuable improvement.

Luxuries are always visible from the start, so this scenario can never come up.

Never ever build a Great Person on a luxury.

In fact Salt is the main exception to the try to settle on luxury rule.

And the strategic resource improvements are normally good enough that most people avoid placing a Great Person on them as well, (it's just that it would be terribly frustrating to have an academy on a tile for centuries and later find Oil there if they didn't)

Some of the bonus tiles tend to popular for Great Person improvements, in particular Sheep and non freshwater wheat.

Edit: NINJAed by above post.