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Please also specify what QGIS version are you using.

Isn't this just the Categorized or Graduated renderer in QGIS?

If not can you post a sample dataset and a image of what you need to achieve.

"Categorized or Graduated renderer in QGIS?"
It might well be - where do I find it in QGIS 1.8.0 menus?

Sample data is at
http://http-server.carleton.ca/~dariush/Microzonation/main.html
Ottawa-Gatineau Shape Files.zip

Found it, Nathan, clicked classify and it shows a range of colours matching the values in the window, but clicking apply then OK doesn't show anything. Do I have to 'add class' or do something else to make it work? There's nothing in the manual about it except to say it exists...

John Sankey wrote:

Found it, Nathan, clicked classify and it shows a range of colours matching the values in the window, but clicking apply then OK doesn't show anything. Do I have to 'add class' or do something else to make it work? There's nothing in the manual about it except to say it exists...

did you choose a proper attribute to make the classification?

John Sankey wrote:

attribute?

in a GIS an attribute is a column of the table that is associated to any vector. To classify your vectors you need to choose an attribute.

Fair enough, Giovanni, but I should clarify: where do I choose an attribute? I can't find anything called that in layer properties; under Column there's only one option, shown. My apologies for sounding dense, but I don't know QGIS backwards and forwards the way you do...

John Sankey wrote:

Fair enough, Giovanni, but I should clarify: where do I choose an attribute? I can't find anything called that in layer properties; under Column there's only one option, shown. My apologies for sounding dense, but I don't know QGIS backwards and forwards the way you do...

try have a look here

http://docs.qgis.org/html/en/docs/user_manual/working_with_vector/vector_properties.html#style-tab

"Categorized Renderer"

Giovanni, I've gone through the manual, at least three times. I've saved a graduated style from the layer properties window with a name. I then click on symbol change; the style I just saved isn't listed on the symbol selector window under saved styles. There's nothing about selecting a style in the simple fill dialog either, which is where I want the renderer to use the saved style. If I open the style manager in the symbol selector window, it shows the style I've saved, but nothing I've tried has applied it to the simple fill symbol.

Might this be a directory problem, that I've saved the style in the subdirectory where the .shp file is, and the .qgs file is in a different directory? There's obviously some connection I'm missing between style and symbol. Is layer style somethiing different from symbol style, perhaps?

You don't need to split the layer. I'll download the sample data and have a look.

Looks fine to me

Lovely! I tried a new project and everything shows fine. It seems that this data is referenced to UTM zone 18N, all the CanVec data is WGS83, and that QGIS 1.8.0 can't show two different CRS's in the same project. All my previous tries I was adding to an existing CanVec-based project so this one didn't show; when I try adding CanVec data to this new project none of it shows.

I'd rather work in UTM zone 18N, but enabling CRS on-the-fly crashes QGIS 1.8.0
Is there any way to hard-convert shapefiles from WGS83 to UTM 18N so everything will work together? Or, do I have to wait for a new version of QGIS for that?

You can change the projection of a layer by using the Save As.. item in the right click menu on the layer. In the dialog you can select a output projection.