Electric Field Lines for Continuous Distribution

I have a doubt about the electric field lines for a continuous distribution. Well, if there's only some point charges, I know that the field starts on the positive ones (or at infinite), ends at negative ones (or at infinity) and the number of lines is proportional to the number of charges. That's fine, but what are the "instructions" to draw the field lines when the distribution is continous ?

I've seem some places where they draw the lines just imagining that the continuous distribution is the same as a finite distribution of small charges $dq$, but I'm not sure that this is the way to do it.

Can someone point out how do we work with this ?

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Are you asking what the electric field looks like within the distribution, or outside of it? – Ataraxia Mar 24 '13 at 19:44
Sorry, I forgot to point this out, I'm thinking outside of it. My problem is: when using Gauss' Law I need to know the direction of the field, so I need the field lines, but I'm confused how to work with it for continuous distributions. – user1620696 Mar 24 '13 at 20:00
The directions of the electric field lines from continuous charge distributions are only easily expressible in cases of high symmetry (e.g. only in a particular region of space), or if it is an infinitely large distribution (e.g. an infinitely long cylinder, or an infinitely long sheet). – sujeet Mar 24 '13 at 21:36