[Qgis-user] Rasterize vector

[Luciano La Sala]

Dear QGIS experts, 

I am using QGIS V. 1.8.0. and I have a shapefile of Argentina which I need
to convert to raster. I looks as a pretty straightforward process, but along
the way I hit the following problem:

1) Once the vector file is loaded, I go to Raster >> Conversion >> Rasterize
(Vector to raster)
2) I select the output file but the following message pops up: "The output
file doesn't exist. You must set up the output size to create it."
3) I hit Ok and then I am left to decide what size do I want for the output
file. The default values are Width = 3000 and Height = 3000.

So at this point my questions are: 

a) What are these values for width and height? What do they represent? After
conversion, I load the raster and under properties and metadata tab it says
that dimensions of raster are X: 3000 Y: 3000 Bands: 1, but I am not sure
what this means. 

Thank you in advance for your help. 

Luciano