What is the location of the center-surround receptive fields of retinal ganglion cells?
A nice illustrative image of how the photoreceptors connect to the retinal ganglion cell (RGC), and thereby facilitate the center-surround structure is provided in figure 1 below. It shows a cross section through the retina.


Fig. 1. Photoreceptor organization and connections to the retinal ganglion cell. source: McGill University   

The receptive fields (RFs) are determined by the number of photoreceptors connected to the RFs. RFs are smaller in the central high acuity area of the retina (the fovea) and increase in size more eccentrically. As a result, visual acuity is highest in the center visual field, and degrades more eccentrically in the field of view.