[fishtoaster]

If I understand map projections correctly, isn't this just whatever projection google maps uses (Mercator) with an overlay?

I probably don't really.

[kilovoltaire]

Yes this is definitely just Mercator. But you could reproject in a Manhattan-relative way, such that this larger grid actually looks like a grid (just like latitude and longitude do in Mercator) and that might be a... pointless new projection.