pawn capture question

A general principal of capturing with pawns is to capture towards the center, but why is it in this situation that it is more advantagious (so i am told) to capature away from the centre. There is another example in the ruy exchange:

Why capture away from the centre?

Half opens d-file for Q, and allows bishops onto QB1-KR6 diagonal?

I'm sure the bxc vs dxc continuations have been analyzed extensively for both openings, particularly the Ruy... so one answer is: because analysis says dxc is better...

but in both positions I think general chess sense should lead one toward dxc over bxc.   In both positions the dxc capture liberates Queen and Bishop, and avoids isolating the a-file pawn.  In general, in open games, piece activity is crucial. dxc is more activating and leaves the pawns in better shape. (And If you can avoid giving your opponent targets, do.)

I always take the advice to take toward the center to really mean: think carefully about which way you want take and if you can't find good reasons not to -- take toward the center.

In the first example the open d and e file give white easy play, with opportunities to castle long and attack black on the kingside. The pawn on c3 then gives white a bit of extra defense for if black tries to attack the white king.

I'm not too sure about the second example, but from a positional perspective it's probably better to have two pawn islands than 3 (and the a pawn would be isolated so possibly weak)

One last consideration is that you allow your queens bishop to devellop

For one thing, bxc makes the pawn structure more potentially weak, at least if black ever attempts to exploit his decision and play a quick ...d5. Another problem is that black is slogging in development now, and since there is no control of the center for black aside from the e5 pawn, white is free to take it with d4. Playing ...dxc6 keeps the structure solid (though it gives white a k side majority, good for an endgame), opens up lines for the bishops right away, and the open d file allows black to react to d4 in a decent way, and that way his bishops are open. The ...d5 plan after bxc is too slow and cumbersome.

I think this is an excellent way to think about it. If I can think of good reasons to capture away from the centre, I will. If there aren't any compelling reasons, capture towards the centre.

Capturing away from the centre happens early in several openings to facilitate development, which is a good reason.

 No that is not the reason. In the first example ((Petrov defense) (that is by the way not the main line)) it is perfectly acceptable to play bxc and in fact a more experienced player might. It all depends on your style. In the second example YOU ARE FORCED to play dxc so yuo dont lose material I shall illustrate:

1st one in the petrov the idea is to castle queenside get the dark square bishop out to f4 and start a pawn storm on the kingside

2nd one ruy lopez exchange the queen can come out so you dont lose a pawn for nothing

No, after ...bxc6 Nxe5 either ...Qg5 or ...Qe7 ( or if it really doesn't work as you said, just ...Qg5) should still win the pawn back.

@ zxb995511  (*edit* sorry about the misdirect, elubas, my mistake!)

.... In the first example ((Petrov defense) (that is by the way not the main line)) it is perfectly acceptable to play bxc and in fact a more experienced player might. 

Really? It looks like crap to me, but I'm not going to argue with book.

*edit* I just did a quick check with the game explorer and dxc3 is preferred to bxc3 in something like 700 to 10 games and bxc3's stats are much worse... what are you basing your opinion of this move on? 

edit #2: here's how it looks in my database:

    Move   Frequency      Score    AvElo  Perf   %Draws
 1: dxc3    2350: 97.9%   62.7%    2325    2378   40%
 2: bxc3    47:    1.9%     45.7%    1977    1982   23%

 In the second example YOU ARE FORCED to play dxc so yuo dont lose material I shall illustrate --

I agree it's essentially forced -- but as has already been pointed out Black can win the pawn back... but if White plays Nxe4 what we get for Black is rather like a busted Petroff's defense, busted because his Queenside pawns are compromised. It's not a simple material loss... it's a positional/structural problem for Black.

 Do you mean zxb995511?