This is the cool city level you might already have seen some screenshots of. You start out in a subway station with several parallel train lines which are connected by some intersections. As getting through this tunnels to the city entrance seems to have been more of a challenge to several people than I expected I'm going more into detail.

The trains run in different patterns so you got to wait and watch till you get the hang of them. Keep checking the map or use the Guidebot on which direction to go to the city entrance. Sometimes you'll have to wait on a passageway beside the train line for the next break in the pattern. Just for fun turn on your rear view to see how close the next one is on your heels. BTW, you can also fly under the trains or hover above them, there are some "niches" where you can fit in seamlessly. However, if you don't level you ship correctly you might get blown. As this technique forces you to watch for the train patterns anyway I suggest you use the aforementioned method.

The arrows show the direction the train is coming from whereas the points between the numbers show the breaks between the trains. The more points the more time you have till the next train arrives.

Once you've reached the city almost everything works by itself, just keep your eyes open for those powerups. To get the fullmap enter the sewers at the other end of the city, turn right immediately and follow the main tunnel till the end and fly up. At the end of the large hall you'll get the fullmap which should lead you to the PTMC headquarters; it also reveals a secret area in this level. Left of the entrance to the headquarters you'll find a secret door below an eye on the wall that leads to a Chinese Garden. BTW, there's an invulnerability on the wall which is quite helpful against those mercenaries.