Very good table though you know I think you will have some trouble to keep this level of detail with the development of our cities and the number of units and improvements available. 
For the sake of clarity I would not seperate the queue and the time needed, I would write it like that:
Catapult (4). In the same spirit I would not write anything when the given type of improvement or unit is not in a city (especially when improvements are concerned) and I would simply put an "X" in the box to indicate that the said improvement has been built in this city. Tables can be difficult to read with too many figures or informations.

For the sake of clarity I would not seperate the queue and the time needed, I would write it like that:
Catapult (4). In the same spirit I would not write anything when the given type of improvement or unit is not in a city (especially when improvements are concerned) and I would simply put an "X" in the box to indicate that the said improvement has been built in this city. Tables can be difficult to read with too many figures or informations.

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