Locus: sNye-thang (Central Tibet)
Atiśa to rNgog: “O Legs-pa’i-shes-rab, you should construct a monastery on the slope (phu) of this region. Study of logic and epistemology will flourish” (legs pa’i shes rab khyod kyis lung pa ’di’i phur dgon pa zhig thob dang | tshad ma’i ’chad nyan dar bar ’ong).
rNgog to Atiśa: “Well then, [I] request you to keep it a secret for a while” (’o na re zhig gsang bar zhu).
That is why the place/monastery is called gSang-phu. See the Bla brang gdan rabs (p. 272).