Law

 Overwatch, sometimes called Hall of Justice:

Basically I got the idea from where I was introduced to Simcity 2000, where, if you build enough arcologies, crime foes way up. But I was like "These standard police stations really disrupt the futuristic vibe..."

1) Strictly speaking, the Overewatch is not an arcology at all. People largely don't live there. it does not produce its own food. It recycles water, I guess. But it is an imposing superstructure. But think of it as the stacking of all the major municipal buildings into one building.

2) It is found in the center of the city, every train runs to and from, sometimes redundantly. First responders exist in every deck in every arco, but this has an elite auxiliary. Police, Fire Brigade, even paramedics are stationed there (Every second counts, and the medical needle usually has some other logic behind where it's positioned.)

3) Also, because it houses most of the major government offices (They actually speficcally house a few departments and deputy positions in other arcos just for safety reasons) they want to make it look like anyone who wants to break in and burn it down...can't.

4) It's a police Academy but also...a law school. Sort of like Judge Dredd, but in a less reactionary way, going into lawn enforcement means a Pre-Law education. If you want to hit people with a stick, there's plenty of other jobs. But they also need to representatives of the court to act incredibly fast in such a dynamic and condensed society where people lived in closed loops.

5) This is actually drawn a little from how for instance, in Rhode Island the Sheriff is strange blurring of law enforcement and the Judicial Branch. Overall, this creates an interesting mix of law enforcement who can be real eggheads (Like Tom Hanks's FBI Agent in Catch Me If You Can) and lawyers who are two fisted, country style folk. (Think Abraham Lincoln). That's generally what detectives act like: FBI Agents, since in general 

6) The Forensics and crime research lab is pretty extensive, in fact a lot of people join law enforcement because they want to work in a lab but are afraid their paths might lead them to some creepy alien biome.

7) This is also the vault for any solid assets (usually gold or the like) for municipal treasuries, banks, etc, as well as mainframe data centers for national and public banks.

8) Also, this building houses a library, a massive, massive library. They try to keep a hard copy of everything. Court transcripts. News clipping. Top 40 songs. Available to the public. This creates a system of transparency. But arguably corruption, because it's very easy to hide paper trails in plain sight, it's like taping together shredded documents.

9) There's commissaries and a couple other commercial stations, but alcohol is prohibited from being sold, though every desk has a flask, just about.