this is the forest brush I've been using lately for my satellite style maps
(i just realized it's 5 megs, yow. i don't remember the texture being that large, what the heck! the site won't let me upload it. so drop box to the rescue.. turns out that the compressed version is almost the exact same size, so i'm not bothering with a zip file..)
Assuming you're using a tablet and photoshop, pick out your clone stamp tool, load tool presets from wherever you saved the file and then click on the "forest" brush. If you're using a tablet, it's all set for pressure sensitivity, if a mouse, you may have to tweak a few of the brush settings. If this is on it's own layer set to multiply then it should work nicely - at least it does for me.
Basically it's a 17px torn edges brush with a moss texture built in with size jitter and scatter properties attached to pressure sensitivity.
As to bridges, the only city map I've done in a similar style utilized Ascensions city tutorial, might be worth looking into