To add to Greebo's explanation...
When you create a spawn in the TE, the direction of the spawn from the base determines the direction you face when spawning. If you spawn NE from a base, you will be facing NE when you materialize. I tested this while building a little tanktown spawn on a map I built, and along with this, I noticed there were approx 3-4 positions within the spawn radius that I would spawn into.
