Why does game let me build both a harbor and commerce districts.

[MarkJohnson]

I keep messing up and building a commerce district and harbor. The game says you only get benefit from 1. So, why does it let me build both? Shouldn't it lock me out?

Are there some special abilities out side of this that make it worth to build both?

[Copernicus]

Both are valuable; you can only get a single trade route even if you have both, but both also generate revenue independent of each other.

Harbors also provide naval unit improvements as well as Great Admiral points. Commerce districts provide Great Merchant points.

Also, a Commerce district built adjacent to a Harbor district receives an additional bonus to revenue.

[Evrach]

No, that's the opposite. You get benefit for both commercial hub and harbor except one : the trade route. You'll unlock one trade route after having built the first building of either the commercial hub (market) of the harbor (lighthouse). But if you build a Market and a Lighthouse, you won't get two trade routes.
For all the other bonuses, you cna have both.

[MarkJohnson]

OK, I thought I was only able to benefit from either the harbor or the commerce district. This makes much more sense. I get everything except only 1 trade unit, instead of 2.

And to get an extra bonus back, I must build commerce next to harbor for extra gold bonuses.

Thanks for your help

[jmerry82]

Originally posted by Evrach:

You'll unlock one trade route after having built the first building of either the commercial hub (market) of the harbor (lighthouse).

This is ruleset-dependent; under the "vanilla" rules, you get the trade route just from building either a commercial hub or harbor. Still only one trade route per city, though.

[colostmy4]

Originally posted by Copernicus:

Both are valuable; you can only get a single trade route even if you have both, but both also generate revenue independent of each other.

Harbors also provide naval unit improvements as well as Great Admiral points. Commerce districts provide Great Merchant points.

Also, a Commerce district built adjacent to a Harbor district receives an additional bonus to revenue.

You can also get some food production from buildings in the Harbor District

[plaguepenguin]

The Owls of Minerva in Secret Society lets you get two trade routes for having both a harbor and a commercial hub in the same city.