Yesterday, @Maxar released a really high-quality images of the changes at Natanz from October 21. @rafaelmgrossi has said that Iran is building an underground centrifuge assembly facility. We don't quite know, yet, where the facility will be located.
One school of thought is the facility will be a shallow "cut-and-cover" facility like the enrichment halls at Natanz. Another school is that it is more likely to be a located in a tunnel, like the enrichment halls at Fordow.
So far, there is no evidence of tunneling -- just road construction. That could either mean that the facility will be built elsewhere or simply that it is very early in the process and tunneling has not yet begun.
That leaves the question of whether the construction activity at this site is for a cut-and-cover centrifuge assembly building or support camp for road and tunnel construction.
Some of the arguments for this being the site are: The area was enlarged allowing it to accommodate a structure as large as the destroyed centrifuge assembly building (50x80 m), it sits in a depression that could be covered, and the halls at Natanz are also cut-and-cover.
Some of the arguments for this being a support area are: One must also explain the road leading into the mountains, a horizontal tunnel offers greater protection from aerial attack, and there are no obvious signatures of a new building going up yet.
It's fun to debate which is more likely, but it is also a little pointless. We know what Iran is building and as construction progresses (and more pictures are taken), we'll find out the answer.
This is a common problem in an era with so many high- and moderate-resolution imaging satellites -- we often catch construction of new facilities in the vey early stages, well before it is possible to fully characterize them. Which is a nice problem to have. If you are patient.
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