Sometimes the center is the capital of the nation that contains the tribes or at least a part of several tribes. Tribes do not fit neatly into boundaries. Think of the native Americans in Alaska or Canada and the Pacific Northwest. That is the picture in Central Asia.
However, the urban center usually has the greater advantage when the artisan wishes to produce a product with an organic unity, such as an important piece of jewelry. I have posted several times on the symbols and their meanings expressed in silver and gilded silver jewelry among the Turkoman tribes. Here is an expression of their reverence for a mountain symbol:
You can see more detailed information on this piece at http://www.artfire.com/ext/shop/product_view/craftsofthepast/4056415/