Its NOT a cheat sorry, i thought it was but it really handy tho. This will show you what you have done, not bad tho, 1st time in the GTA series.
When viewing the map, when you scroll etc. Hold X for 3 secs or longer and you'll see the show discovered extras like red ballons, rampages and unique stunt. Cool eh,you must keep holding X. What a find
EDIT: Sorry, only displays what you done
EDIT2: Sorry wrong bit of the forum