了如指掌 瞭如指掌

    liǎorúzhǐzhǎng

    1. Idiomto know something like the back of one's hand (idiom); to know (a person, a place etc) inside out

    他对这里的每条小巷都了如指掌。Tā duì zhèlǐ de měi tiáo xiǎoxiàng dōu liǎorúzhǐzhǎng.He knows every alley here inside out.