What is the observer's reference frame for this kind of a picture?

[geordief]

https://www.google.ie/imgres?imgurl=https%3A%2F%2Fi.stack.imgur.com%2FiGT6a.jpg&imgrefurl=https%3A%2F%2Fphysics.stackexchange.com%2Fquestions%2F3009%2Fhow-exactly-does-curved-space-time-describe-the-force-of-gravity&docid=FNB641e0gGK45M&tbnid=PbJ8EF-vi9eU2M%3A&vet=10ahUKEwjXuuC9t_LWAhVSaFAKHfP5CksQMwg2KBAwEA..i&w=600&h=458&hl=en&bih=769&biw=1600&q=earth curved space&ved=0ahUKEwjXuuC9t_LWAhVSaFAKHfP5CksQMwg2KBAwEA&iact=mrc&uact=8

 

These grid lines are shown as curved around the massive object that is the Earth.

I appreciate that they are an attempt to show 4D and so this picture is non representative (very incomplete) on that account but I want to ask specifically  what observer could have drawn those lines?

Someone far removed from Earth's gravity? That is how such an  observer would draw a "straight line"  in the vicinity of the Earth? An observer on the Earth would draw different  "straight lines"? Correct?

Edited October 15, 2017 by geordief