Apollo and I were working on this last month, but I don't think we posted about it. So your post is quite valid and won't be relegated to the GP due to the classic exchange that just occurred between you and Enigma. (That was the GP, BTW!)
An Impromptu Data Hive Mostly-HAQQ: How to I enter the Data Hive mission?
A: Complete the first seven missions (including Prepare to Drop). When this is done, you'll hear Dare talking to you in Mombasa Streets.
Q: Can I explore the entirety of Mombasa Streets instead of playing the Data Hive mission?
A: No. When you finish the first seven missions and hear Dare talking, you become locked into the district that you began your last mission from. Because of this
Data Hive Lockdown, you can only explore one district while Data Hive is active. There is one slight exception to this, noted below.
Q: So wait- I can get locked into different districts?
A: Yup. It all depends on the last mission you complete. Here is where you'll end up depending on which mission you finished last:
- Tayari Plaza: D05
- Uplift Reserve: D09
- Kizingo Blvd: D04
- ONI Alpha Site: ONI + D10
- NMPD HQ: D03
- Kikowani Stn: D00
Q: Wait... does that mean there is more than one entrance into the Data Hive mission?
A: Yup. There are six. Apollo Doom and I began charting them, but that work remains largely incomplete:
- Tayari Plaza: D05
- Uplift Reserve: D09
- Area View (No Photo)
- Door Closed (No Photo)
- Door Open (No Photo)
- Kizingo Blvd: D04
- ONI Alpha Site: ONI + D10
- Area View (No Photo)
- Door Closed (No Photo)
- Door Open (No Photo)
- NMPD HQ: D03
- Kikowani Stn: D00
- Area View (No Photo)
- Door Closed (No Photo)
- Door Open (No Photo)
Please note that all six of the Data Hive entrance locations are marked in the
POGG.
Q: How on earth can I finish my seventh mission with Tayari Plaza or Uplift Reserve? They're no longer active because I had to play them to get to the other four!
A: In a normal campaign mission you will not have the option to end on Tayari Plaza or Uplift Reserve since these missions are prerequisites for unlocking access to Districts 06 and beyond. This changes when you begin the "Mombasa Streets" mission after having completed the game once. In that case, you will begin in the streets with six active missions, including CM:TP and CM:UR.
Q: What do you mean by "ONI Alpha Site: ONI + D10"?
A: If you finish ONI Alpha Site last, you will return to the ONI area. The exit is in the adjacent D10 (through the tunnel). This is the only exception to the rule of being locked in one district, for technically these areas are separately loaded.
Q: What if I have a picture that I took in-game or a map that I made myself of the location of a Data Hive entrance that is listed as "No Photo" above?
A: If you posted it here, it'd be the GP.