To add some context, and detail, each city is better at producing certain goods, based on specific goods provinces that are close to you. The three provinces that form an isosceles triangle around your city, (with one point straight up) are your cities boosted goods. My boosted goods are Marble, Crystal, and Gems.
You can also look in your technology/research tree, where they will be identified as a "production boost" in chapters 1, 2, and 3 right after you get the Manufactory research: