When you create an account the game assigns an initial location for your planet in the universe. This location, or rather the distance from the galaxy core, depends on your race. For example, Baleenars as a mining-oriented race tend to be found near the resource-rich galaxy core while Slithins as a technologically superior yet less war-like race have withdrawn to the outer rims of the galaxy. On the other hand Lilnosas and Mossopps have spread out in practically every corner of the galaxy.
Below is a chart illustrating the possible distance from the core for planets of each race. The possible range is marked with red, and the gray bar indicates areas where the race in question does not live.
Note that, unlike the impression this chart might give, the galaxy is in fact shaped like a doughnut, in which solar systems orbit the uninhabited core, and the distance limitations in above chart apply to all directions in three dimensions. This means that you will be assigned with random x,y,z -coordinates, according to your distance from the core, that are used to calculate your travel times to other planets. Due to this, even if your planet would be located in the outer rim, you might still have neighboring planets where your travel times are very short. Also, due to this structure, the coordinates you see in Universe-screen have nothing to do with the actual location of the planet and as such they serve merely as numerical identifiers for planets.
Since Beta 0.8b the spatial coordinates of planets have not been fixed and are constantly changing because planetary systems move on an orbital path around the galaxy core. This means that your travel times to certain planets might change as the round progresses.
There are certain limitations to travel times between planets so that there won't be ridiculously low or high travel times. Without travel time technologies, the minimum travel time between two planets is 7 hours and the maximum is 16.