Roughly two-thirds of all spirals are observed to have an additional component in the form of a bar-like structure, extending from the central bulge, at the ends of which the spiral arms begin. Our own Milky Way has recently (in the 1990s) been confirmed to be a barred spiral, although the bar itself is difficult to observe from our position within the Galactic disk. The most convincing evidence for its existence comes from a recent survey, performed by the Spitzer Space Telescope, of stars in the Galactic center.
In 2005, observations by the Spitzer Space Telescope backed up previously collected evidence that suggested the Milky Way is a barred spiral galaxy. Observations by radio telescopes had for years suggested the Milky Way is barred, but Spitzer's vision in the infrared region of the spectrum has provided a more definite calculation.
Essentially, the older and larger stars are in the center. Some even speculate that most larger galaxies may have super Black Holes in the center of the Galaxy. Our galaxy has a bulge of older and large stars in the center, and the further you get from the center the fewer the stars. Likewise, gravity also condenses the plane in which the stars orbit the center of the galaxy. The outer rim of our galaxy is (more or less) flat. Our type of galaxy is a kind of galaxy that looks like a flat, slowly rotating disk with a bulge in the centre. Our Solar System is located within the disk, around two thirds of the way out from the Galactic Center, on the inner edge of a spiral-shaped concentration of gas and dust called the Orion Arm.
With all that being said let us think about the "Inner Sphere."
The center of the Inner Sphere (the battletech universe) is Earth. Since we are not very close to the center of the galaxy most of the stars will be (more or less) in the same plane. While there are several exceptions - very few stars will be significantly below or above the plane. Often times a solar system will bob up and down from the plane of the galaxy. As the solar system revolves around the center of the Milky Way galaxy in a period of roughly 230 million years, it does bob up and down through the galactic plane in periods of roughly 35 million years.
Anyhow, it is reasonable to assume most of the inhabitable stars within the inner sphere are located in such a way that if you looked down at our galaxy that you can see all the stars in a 2-D format. Many stars in our galaxy do not (according to Battletech and MechWarrior lore) does not support life. The few that have planets that are colonized are represented correctly in a 2D format, probably.
Edited by Boydsan, 26 April 2013 - 08:31 AM.