There are 11 locations in Star Wars: Knights of the Old Republic (including ships):
Your starting point in the game. A Republic space ship caught in an attack by the Sith fleet. As soon as you escape from the Endar Spire, it immediately blows up, with the only survivors being Revan, Carth and Bastila (although you have not met her yet).
The planet your escape pod crash lands on. A strange world, divided very clearly into the Upper City, Lower City and Undercity. Each level is very different from each other, from the people you meet to the actual setting. After meeting with Davik and killing him, Taris is destroyed by the Sith fleet.
The home to a Jedi Enclave and a peaceful land, with no big cities( that we know of ) and quite a rural place. Later during your quest for the Star Forge, it is later found out that the Jedi Enclave was destroyed by the Sith fleet.
Home to the native Wookiees. A rich and fertile forest land, where the locals live in trees because of the dangers that lurk on the forest floor. Czerka has also set up a small operation here, mainly dealing in slave labour, however due to your decisions during the game, the Czerka station will possibly be overrun by the now rebel Wookiees and they do not return.
You do not actually visit Yavin 4 but a small station orbiting it run by Suvam Tan9, an alien who runs it alone, only occasionally talking to smugglers. He sells the best items in the game. Note: Visit Suvam every time you find a Star Map piece as it updates his inventory.
The Sith homeworld. This is where the original Sith (Naga Sadow, Freedon Nadd etc.) settled down and this the home to the Sith. It is a desolate place and the people there all seem nasty, as if the Dark presence there has corrupted them.
This is a strange jungle world, with the natives being the Rakata, now strange tribal warriors who have existed long before all the creatures but fled underground after their force powers disappeared and their empire had collapsed. This is where you will find out about the secrets of the Star Forge and (Spoiler Warning) this is where the plot lines fork. It doesn't matter your past options, the scene with Bastilla is the one that decides your fate.
This is basically a huge production facility/space station. This is where the Sith had been getting their huge, mysterious number of troops from, and after the duel with Dark Lord Malak, the Republic Fleet destroys the Forge using Bastilla's Battle Meditation, OR, you trick the Republic Fleet, they are destroyed and you take command over the Sith Army.
This is Saul Karath's flagship, the ship responsible for the destruction of the Endar Spire, Taris and the Enclave on Dantooine, this is where Bastila is taken hostage by Malak and causes her to turn to the dark side.