Regardless of whether it is truthful and based on actual science, humanity have been using astrology since the beginning of time. We see the pyramids, Sphinx, stonehenge and a multitude of other big structures heavily oriented towards the sky and what it represented to them.
Using astral mapping and proper calculations, would it be possible to help narrow down new archeological sites that are, just as an example, buried under the sand in the Sahara desert or deep inside the Amazonian jungle?
I think you may be confusing Astrology for Astronomy. Many ancient cultures like we do today, looked to the stars and were proficient Astronomers. The Maya, Inca, and Aztec (Mexica) were among the most notable with charting the astral in South America.
It is possible to "star map" however it's a very tricky process and isn't the most reliable, but it is a tool sometimes utilized by Archaeologists. In the past decade, most notably in mainstream news, a 15 year old applied this logic with the Mayan culture and was able to locate a possibly "lost" (in western terms) settlement; Although no archaeological work has been done to follow up the claim and I have not analyzed his location myself, either.
Many things make the process to locate ancient settlements using the stars an unreliable one. "Who, what, when, where, and why" are very important key tools to apply while researching this topic. 'Who' are you speaking of or researching, 'what' star cluster are you referring to, 'when' was that star cluster locally relative to your 'who' and then, 'why'. What, When, and Why are very important. Due to the rotation of the Earth, our stars, relevant to us, move. Throughout generations, local star clusters relative to a specific location, change. It is also very difficult to match up a specific star cluster to a specific culture. What the Greeks saw as the constellation Scorpius, the Javanese people called The Leaning Coconut Tree; to the native Hawaiians, it is the Big Fishhook of Maui. So while it is possible to use star mapping, it's not too plausible due to it being unreliable by nature, now.
When you speak of the ancient Saharan desert and Amazonian rainforest, you are referring to a time frame roughly ~12,000 years ago; to the Mesolithic and Neolithic periods. We are only now learning and theorizing (with evidence) what those cultures and landscapes might have been. This is a time frame that I am absolutely fascinated by and hope to help further the research coming out of those two regions.
I hope this helps serve as answer to your question! If you have any more questions I'd totally love to discuss this further!