It took me a while to figure out that tile bonuses (like "Caverns" and "Planetfall") applied one bonus to their own tile and another bonus to an adjacent tile. I think this is for two reasons: inconsistent icons and not being directly noted in text.
First, the bonus itself should probably be labeled "+1 Bonus to Nearby X" rather than "+1 Bonus to X".
Second, the four-arrow icon is inconsistent in usage. When you build something like the Manufacturing Capital, it is labeled "Bonus to Adjacent Improvements", <GREEN ARROW> +3 to Manufacturing. If the four-arrow icon is intended to mean adjacency bonuses it should be used for structures as well as the native tile bonuses.