Getting the Most Out of QGIS and GRASS Integration - Desktop GIS: Mapping the Planet with Open Source Tools - page 220

The full option list for the command is as follows:

GRASS 6.2.2 (albers_c6):~ > r.contour help

Description:
Produces a GRASS binary vector map of specified contours from GRASS
raster map layer.

Keywords:
raster

Usage:
r.contour [-qn] input=name output=name [levels=value[,value,...]]
[minlevel=value] [maxlevel=value] [step=value] [cut=value]
[--overwrite]

Flags:
-q Suppress progress report & min/max information

-n Suppress single crossing error messages

--o Force overwrite of output files

Parameters:
input

Name of input raster map

output Name for output vector map

levels List of contour levels

minlevel Minimum contour level

maxlevel Maximum contour level

step Increment between contour levels

cut Minimum number of points for a contour line (0 -> no limit)

default: 0

Note we could have specified both minimum and maximum contour lev-
els, as well as an interval and a step value. There is also a cut option to
specify how many points constitute a contour line. The point of show-
ing you the GRASS usage of this command is this—don't count on the
QGIS-GRASS modules to provide you with all the options for a particu-
lar operation. For this reason, it's good to always read the manual entry
(available from the Manual tab for each module) to see what you might
be missing.

Map Algebra
If you've been following along with QGIS and actually opened the tool-
box, you're probably thinking “Wow, there's a lot of modules in there.”
You're right, and there is no way we are going to give you an example of
each. The goal is to get you started with the basics, and you can develop
your skill set to meet your needs. That said, there is one last module
we want to look at, just because it's a bit different from the others.