There are 3 levels to the map.

Top level (When you first log in) is referred to as the Galaxy level. If you double tap a galaxy location you will then drop down to the sector level, this is always a 25x25 map. If you then double tap a sector on the sector map you will go to the system level. This level is where you will see the planets.

You can fly anywhere you want on the map. If you click a ship and go all the way to the galaxy map, you can click on any location and go to that locations sector map then set a destination there. Your ship will fly there, assuming you aren't trying to fly through the core (center of the galaxy level)