Explanation: We already know that N(location)にNがある means “there is [a] N [on/in…] N(location).” Using the -te form of a transitive verb shows what somebody did to the thing to get it there. Examples:
- 机の上にメモが置いてあります。
A memo has been put on the desk.
- カレンダーに今月の予定が書いてあります。
This month’s schedule has been written on the calendar