There are many infrastructures which provide something like "+X food on river tiles" or "+X production on wood/forest".  These are very tedious to evaluate as it is usually not clear how many of a given terrain feature the city is currently exploiting.  This requires the player to go and manually count each river hex in/adjacent to the city, then count each woodland/forrest hex in/adjacent to the city, etc.  

It would be very helpful if the tooltip for these buildings indicated something like "actual: +X production" which would simply do the counting for us (under the CURRENT city conditions).