Strat-map editing: Rivers/Land features

[Ciaran]

All, right, I know technically where they´re supposed to be made, and I even know how, but what I´ve got difficulties with is actually implementing that knowledge...
The problem is, while Photoshop is a great tool for all sort of image-editing stuff, one thing seems impossible to do: Adding one single pixel or a single-pixel line (important for rivers, river crossings, city and port positions...), without any spillover effects on neighbouring pixels. It drives me mad. A program like Paint can do it, for Gods sake! So why not such hgh-and-mighty thing like photoshop?
So, what am I doing wrong? Or rather, how do I do it right?

[Lord Adherbal]

use the pencil, not the brush, it doesn't do anti-aliasing

[nikolai1962]

Or set the brush to 100% hardness (i think that's the one). It doesn't smudge the colours then.

[Ciaran]

use the pencil, not the brush, it doesn't do anti-aliasing

I was missing that particular tool, I didn´t know you had to switch between brush and pencil. Thanks (mostly for confirming that a pencil tool actually exists).