These [Slokas][1] from the Brihat Parasara Hora Shastra introduce the 16 types of charts (Shodashavarga) to be used for analysis

> वर्गान्‌ षोडश यानाह ब्रह्मा लोकपितामहः।
> 
> 
> तानहं सम्प्रवक्ष्यामि मैत्रेय स्रूयतामिति॥ २॥
> 
> क्षेत्रं होरा च द्रेष्काणस्तुर्यांशः सप्तमांशकः। 

> नवांशो दशमांशश्च सूर्याम्शः षोडशांशकः॥ ३॥

[Translation][2]

> 2-4. Names of the 16 Vargas. Lord Brahma has described 16 kinds of
> Vargas (Divisions) for each Rāśi. Listen to those. The names are Rāśi,
> Horā, Dreshkana, Chaturthāńśa, Saptāńśa, Navāmśa, Dashāńśa,
> Dvadashāńśa, Shodashāńś, Vimshāńś, Chaturvimshāńś, Saptavimshāńś,
> Trimshāńśa, Khavedāńś, Akshavedāńś and Shashtiāńś.

Here, the natal chart is called the Rasi chart. In various other chapters, Rishi Parashara explains how to use these. 

There have been many subsequent texts by Jaimini, Saravli, Manterswara etc which give elaborate details on how to use the natal chart and the other charts.


  [1]: https://sa.wikisource.org/wiki/%E0%A4%AC%E0%A5%83%E0%A4%B9%E0%A4%A4%E0%A5%8D%E0%A4%AA%E0%A4%BE%E0%A4%B0%E0%A4%BE%E0%A4%B6%E0%A4%B0%E0%A4%B9%E0%A5%8B%E0%A4%B0%E0%A4%BE%E0%A4%B6%E0%A4%BE%E0%A4%B8%E0%A5%8D%E0%A4%A4%E0%A5%8D%E0%A4%B0%E0%A4%AE%E0%A5%8D/%E0%A4%85%E0%A4%A7%E0%A5%8D%E0%A4%AF%E0%A4%BE%E0%A4%AF%E0%A4%83_%E0%A5%AC_(%E0%A4%B7%E0%A5%8B%E0%A4%A1%E0%A4%B6%E0%A4%B5%E0%A4%B0%E0%A5%8D%E0%A4%97%E0%A4%BE%E0%A4%A7%E0%A5%8D%E0%A4%AF%E0%A4%BE%E0%A4%AF%E0%A4%83)
  [2]: http://bphs.blogspot.com/2007/12/ch-6-sixteen-divisions-of-ri.html