I just "love" those achievements when you have to use a map and search for X amount of things in the open map. Those achievements would be pain in the ass if you have to do them on your own, luckily there are usually tutorials and maps available for the secret locations in the internet.
Wheelman is quite old game and some of the online tutorials have unfortunately vanished - the game is 4 and half years old by now. I found some forum posts with some map images (and some images missing from the imageshack host. I found some other images with no descriptions. Putting 2+2 together gives more or less complete picture of the locations. Unfortunately at the end of getting near 100 locations discovered I see that I seem to have 2 missing. Now I am not sure if to start game again and search for the damn cat statues again to be 100% sure I have got all ... or revisit every location where the cat is supposed to be, but as the instructions are not very exact, no way of telling is the missing few cats supposed to be there or are they collected already.
When I was bored with cat hunting, I did some hot potato side-missions and got 1 achievement.