Most of the action occurs on a fictional island, eight miles long and one hundred miles off the west coast of Costa Rica. Technically it's not an island, but "a seamount, a volcanic upthrusting of rock from the ocean floor" (2.15.9). Sounds kind of prehistoric already, right? Hammond was able to acquire it because it's "very rugged" and the "combinations of wind and current make it almost perpetually covered in fog" (2.6.61). Great place to hide dinosaurs, right? We assume no Google Earth camera vans ever made it there. The mountains and forests would make that difficult, no doubt.
The island itself is divided by moats, roads, and electric fences into sections, each one housing a different kind of dinosaur. It kind of has the feel of a zoo, only with military fortifications, and, you know, dinosaurs. Almost all of the island is monitored by cameras, but these prove to be inadequate when the dinosaurs escape. The sections of the park not under surveillance—like the river—are all connected, so dinosaurs and survivors can move freely, undetected by the control room personnel.
When the story begins, Jurassic Park is still under construction. The control room, engineering labs, and Hammond's bungalow are built, but the hotel and other resort buildings still need work. Eventually, the island was meant to incorporate the features of a zoo, a nature preserve, an amusement park, and a luxury island resort.
In the movie Jurassic World, we finally get a sense of what Hammond's dream would look like when finished. Until everything goes wrong, of course.