The layout you showed looks like what's called copper-backed coplanar waveguide (CBCPW). That means the ground return for the waveguide is not just in the coplanar grounds (the ground fills on the same layer as the signal traces) but also in the plane layer immediately "below" the signal layer. This structure is fairly esoteric, in the sense that I've only seen it used in digital systems when data rates exceed 20 Gb/s.
I found what looks like a reasonable discussion on the differences between CBCPW and microstrip in a Microwave Journal article by Rogers Corp engineers.
This article shows that the CBCPW has lower loss than microstrip at frequencies where radiation loss becomes important in the microstrip, roughly from 25 GHz and up, which explains why CBCPW is not widely used at lower frequencies.
Addressing your question, the article points out some special requirements for grounding vias in CBCPW structures:
For proper grounding, CBCPW circuits employ vias to connect the top-layer coplanar ground planes and the bottom-layer ground plane. The placement of these vias can be critical for achieving the desired impedance and loss characteristics, as well as for suppressing parasitic wave modes.
This basically means that without frequent stitching vias between the coplanar ground and the backing ground, power could be transferred to undesired propagation modes, which would cause either excess insertion loss or strong dispersion in the transmission line characteristics.
It looks pretty reasonable to me. I've got a question and a comment.
What are the components between the antenna and the GPS module? Any clocks etc? If they are power supply lines, it looks a little light on bypassing.
I'd also drop a dozen or so ground vias under the antenna itself, placed randomly. The reasoning behind this is to make sure you don't create a resonant cavity under the antenna, with the walls formed by ground planes top and bottom, as well as the via holes running around the outside. Unlikely, as your pcb is likely to be lossy, but you'd hate to hit the jackpot with that.
Best Answer
Edit: In the case of an antenna ground plane, if the ground plane is too short, your radiation pattern might change and the directivity might decrease. In this case, by increasing the ground plane size you will achieve a higher directivity, and therefore your received power will increase. Then, your Signal-to-Noise Ratio (SNR) will increase, and it will be seen as a reduction of the noise.
Since a GPS antenna is pointing to the sky, it is true that if you increase the ground plane size you will reduce the backlobe of the antenna, so you will be receiving less thermal radiation emitted by ground.
Note: If the "noise" is generated by other devices behind the ground plane, then you could be reducing the coupling between the antenna and that "noise" source, but formally this is not noise, it is an interference.
By adding these vias you are trying to contain the electric field in the dielectric below your transmission line, that is, you are trying to reduce the coupling with other elements:
This is specially important not only in amplifier chains, where you are in risk of retro-alimentation and then unwanted oscillations, or in switches, where the coupling can be higher than the switch isolation, but also in oscillators, in filters, mixers...
Or at least this is what I think...