Walgreens lets you order 2' x 3' posters for $30 each, but you would just want to make sure the image quality is high enough to look good blown up to that size. I don't know how Google Earth photos would look blown up large. I suppose it depends on how zoomed in you are, which depends of course on how big the farm is. Zoomed in on a 40 acre parcel would give you more detail than zoomed out on a 400 acre farm.