There are 20 Unique Jumps in Liberty City. Many cars are suitable for most of these, but if you are having trouble try grabbing a fast car like a Cheetah.
Portland has two jumps accessible near the start of the game.
The next four are found near Trenton and the harbor.
Two jumps are adjacent at the Portland end of the Callahan Bridge.
One jump is under the Callahan Bridge on the Staunton side, and the other can be reached by driving along a grassy median.
Use the stairs inside Bedford Point's tw@ cafe for one jump, and drive a fast car off the roof of the Newport car park for another.
Four jumps are nicely arranged around the Francis International Airport.
The last four jumps are dotted around Shoreside. Two originate in the same parking lot near the dam, and the other two involve jumping over the water separating Wichita Gardens and Cedar Grove from Pike Creek.