Motivated by notions from coding theory, we study the generalized minimum distance (GMD) function δI (d, r) of a graded ideal I in a polynomial ring over an arbitrary field using commutative algebraic methods. It is shown that δI is non-decreasing as a function of r and non-increasing as a function of d. For vanishing ideals over finite fields, we show that δI is strictly decreasing as a function of d until it stabilizes. We also study algebraic invariants of Geramita ideals. Those ideals are graded, unmixed, 1-dimensional and their associated primes are generated by linear forms. We also examine GMD functions of complete intersections and show some special cases of two conjectures of Tohȃneanu-Van Tuyl and Eisenbud-Green-Harris.