liǎo​rú​zhǐ​zhǎng

know thoroughly

Senses

了如指掌 liǎo​rú​zhǐ​zhǎng know thoroughly

idiom · to know something or someone extremely well; to be intimately familiar with something, as if looking at one's own palm

他对这里的地形了如指掌。

References

variant 了如指掌/瞭如指掌 了如指掌/了如指掌
see 了若指掌/瞭若指掌 了如指掌/了如指掌