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

这里地形了如指掌

duì zhè​lǐ de dì​xíng liǎo​rú​zhǐ​zhǎng.

He knows the terrain here like the back of his hand.

Frequency

Written text
0.132 per million

Sources

Frequency data
BCC Corpus (BLCU)