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Note that you are using documentation from 2011. Since then QGIS has advanced to version 2.x and there was a Python API break between 1.7 and 2.0. You can find an up to date description of the plugin creation process as http://anitagraser.com/2014/04/26/getting-started-writing-qgis-2-x-plugins/
Here is one example from the John Hutton Institute in Aberdeen (formerly The Macaulay Institute - where I headed up their commercial GIS team, though didn't create this game), Scotland, which might provide some ideas.
Rasters are made of pixels, and pixels can only store one value. If you need to store more than one value with rasters, you need more than one pixel at each location. For storing different types of information in a single raster, you use several bands. The rasters are called with different names depending on the softwares : multi-band, raster stack, vector ...
Paper version of ERDAS Field Guide is very good. Nowadays it is wikified http://wiki.hexagongeospatial.com/index.php?title=Main_page Older PDF versions seem to be also available for downloading and for free.
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