Wat Yang, or the Monastery of the Rubber Tree, is a defunct temple situated on Ayutthaya's city island outside the Historical Park in the Pratu Chai Sub-district.
The monastery is mentioned on a map drafted in the 19th century by an unknown surveyor. Wat Yang was situated between Khlong Pratu Thep Mi (1) and Khlong Pratu Jin (2), north of the old road linking the Nang Hong, Lion, Wanon and Talat Jin Bridges. Wat Pa Sak was southwest, Wat Noi was south opposite the road, and Wat Noi Nang Muk (Wat Mae Nang Muk) was north. The map indicates no presence of a stupa.
Wat Yang stood somewhere between Wat Pa Sak and Wat Mae Nang Muk, which are both located on or near the property of the Ayutthaya Wittayalai School. I conclude that Wat Yang must have been standing somewhere in this area and thus on the school premises.
Phraya Boran Rachathanin (PBR) shows no unknown structures in the area located between the two canals Khlong Pratu Jin and Khlong Pratu Thep Mi. We can conclude that either there were no traces anymore from this temple in PBR's period or that the drafter of the 19th-century map wrongly indicated the position of this monastery (in fact, the 19th-century map is far from being proportional).
I guess Wat Yang could have been approximately located in geographical coordinates: 14° 21' 3.06" N, 100° 34' 2.14" E.
Footnotes:
(1) Khlong Pratu Thep Mi was situated on Ayutthaya's city island outside the Historical Park in Pratu Chai sub-district. The north-south running canal had its mouth at the old Lopburi River opposite the mouth of Khlong Phraya Phan, leading to Wat Phraya Kong and Wat Phraya Phan. The canal was fed by the waters of Bueng Phra Ram, which in its turn was filled by the waters of the Lopburi River via the Lam Khu Pak Sra. The canal passed the fortified city wall at the Thep Mi Gate, also known as the Khao Semi Gate, a large watergate. The canal has been filled up after the fall of Ayutthaya (1767 CE), and only a few traces of the waterway are left today.
(2) Khlong Pratu Jin, or the Canal of the Chinese Gate, is part of a waterway running through the middle of Ayutthaya from north to south. The canal ran from the Chikun Bridge to the Chinese water gate (Pratu Jin), one of the eleven water gates at that time and was an extension of Khlong Pratu Khao Pluak. The canal was a shortcut through the oxbow of the Lopburi River and connected the old Lopburi River, present Khlong Mueang in the north with - what is today - the Chao Phraya River in the south. The canal could have been the eastern defence moat of the initial city.
