I'm trying to get QGIS (1.8) to scale the point markers for each town in a district proportionately to the size of their population (i.e. bigger population = bigger circle). I can get them to vary by colour by graduating the properties for the layer with the population data. When I try to use Advanced>size scale field function though I either get nothing or the entire screen goes one colour. I've not found a way in QGIS to scale by size only which is what I really want to do. Ideally I want the circles to graduate in size only and to have the same colour. I'm hoping that there is a straightforward way of doing this in QGIS.
Advanced - Size Scale field is the correct way to go. Note that the size you specify in layer properties is multiplied by the value in the attribute field that you choose. Therefore you might want to calculate a new size scale attribute field e.g. dividing population counts by 100,000 or a million.