The Opening Compass

Where do you think the reti (1. nf3 d5 2. c4) would belong to?

It depends a lot on both sides play:
Black has 4 main responses against the reti which are:
e6
c6
d4
dxc4.
e6 and c6 both tend to lead to positional and solid games, specially if white transposes to a queen's pawn position by playing d4. 
White can also play systems like: 1. nf3 d5 2. c4 c6 3. b3 nf6 4. bb2 bg4 (capablanca variation) 5. e3 e6 6. be2, followed normally by castling, d4, nbd2 and Ne5 ideas, leading to positional games.
A bit more aggressive is in the wimpey system move order with: 1. nf3 d5 2. c4 e6 3. e3 nf6 4. b3 c5 5. bb2 (wimpey system) nc6 6. cxd5 exd5 and then 7. bb5, which is also positional but a bit more aggressive 
d4 is the sharpest but it also really depends on both side plays.
after d4, white's best choice is 3. b4, kinda like a reversed pseudo-benko. I used to play 3. e3, however the move 3. nc6 is kinda depressing. 
Now, depending on what black plays after 3. b4, is how the game is going to go: Let's see black's options: 
3. nf6 and 3. bg4 are kinda correlated, but can lead to different positions. After 3. bg4 white can play 4. Qb3, followed normally by g3 which leads to balanced positions most of time, not that aggressive but not that solid either. 
after 3. nf6 white can still play Qb3 but also can play stuff like 4. e3, which can transpose into reversed blumenfeld if black plays c5. but black also has the option of playing 4. e5
3. f6 lead to more tactical and aggressive positions. It's one of the sharpest lines in the reti. 
White usually plays into 4. e3 and after 4. e5 5. c5 and 5. a5, white usually plays Qa4+ but also white can play bb2. 
Qa4+ is kinda a long line and a lot of moves are forced there, white sacs a pawn but gets enough compensations and it's tactical and aggressive IMO. Bb2 is kinda an unexplored idea so i don't have that much of a clue, except that there is an early draw line:
after 6. bb2 dxe3 7. fxe3 axb4 8. d4 e4 9. nfd2 f5 there is 10. Nxe4, and if black recaptures instead of nc6 then White can go perpetual check with Qh5-Qe5-Qd5
C5 line (michel gambit) Often transposes to the reversed blumenfeld because it allows white to play e3. 
dxc4 is a line where white gets more aggressive positions and more attacking possibilities, but black can still solidify with correct play. 

About the reversed blumenfeld lines:
If black accepts the gambit with dxe3 followed by cxb4, i'd say is the most aggressive and tactical line in the reti opening. White has a central pawn mass and is aiming to push these pawns. Black has to play accurately to stop that, and white can eventually create some threads specially with the queen and the rooks. 
If black declines the gambit with nf6, i'd say is the most positional and solid variation of the reti, specially if white continues with the move b5. 
The move b5 can essentially lead to some positions like this:

According to the lichess database, after the move nf6 in masters level and b5, more than 80% of the games end in a draw 

So in resume:
Reti opening (1. nf3 d5 2. c4) in the opening compass:
-e6 and c6 lines: Positional and solid
-e6 lines with the wimpey system: Balanced, trending to be slightly more aggressive and positional
-advance lines with 3. nf6 and 3. bg4: Balanced, also slightly more aggressive and positional
-advance lines with 3. f6: Aggressive and tactical
-Reversed blumenfeld gambit accepted: Aggressive and tactical
-Reversed blumenfeld gambit declined with nf6: Solid and positional
-Dxc4 lines: Balanced, but often leads to more aggressive and tactical positions than solid ones.

Very interesting concept.

First of all, I don't know how anyone can claim KID is more positional than tactical. There are a trillion tactics everywhere. While positional play does play a part in KID, the positioning is mostly predicated on wild and crazy tactics breaking out at any point. Same with the Pirc and Alekhine, very tactical openings (Alekhine tactics may all be worked out at the elite level, that happens sometimes, but king fianchetto defences like KID and Pirc are tactical at every level).

On the other hand, the Winawar and Scandanavian are nowhere near as tactical - I wonder if someone was trying to talk up the merit of using them as defences and sold it a bit too hard to you but these openings are positional by nature and also not that aggressive. Yes the Winawar is somewhat tactical and aggressive - for a French!!! It's still a french defence and can get highly positional. I also don't know how the Scandanavian can be aggressive and tactical.

Vienna also is much more tactical and should be in red. There's no point in playing the Vienna unless you're going to play f4 at some point, opening up everything in a similar way to the king's gambit.