Since these heavier elements only come from stellar nucleosynthesis, a metal-rich star is made of material that came from a previous generation of stars. A metal-poor star is made of material that has undergone little if any processing. The components merge smoothly into each other with the stellar halo among the disk and the inner part of dark matter halo and the dark matter halo among the disk, stellar halo, and bulge, etc. The bulge is the elliptical-shaped center part of the Galaxy about 1000 to 2000 parsecs in radius. The disk is the thin pancake-shaped part about 400 parsecs thick and 15 to 20 thousand parsecs in radius with the Sun 8000 parsecs from the center.
Some stars continue to form so the disk has some young metal-rich stars.
The stellar halo is a roughly spherical distribution of hundreds of millions of old, metal-poor stars that has increasing concentration of stars toward the center of the galaxy. It is about 20 to 30 thousand parsecs in radius and it may contain small amount of hot gas, but the disk contains the vast majority. Most of the globular clusters are found in the halo and, like the halo stars, the number of them increases toward the galactic center. If the solar system was at the center, you would see approximately the same number of globular clusters in any direction you looked in the sky. Since the globulars are found bunched up in one part of the sky, i.e., they are swarming around some other point in the Galaxy, and we are not at the center.