Hi, > Date: Wed, 19 Oct 2011 15:22:02 +0100 > From: M.E.Dodd <[email protected]> > Subject: [Qgis-user] how to make marker size related to values in > column > To: "[email protected]" <[email protected]> > Message-ID: > <9932a16f9ce9264fac3f2e0e008e12210123c33...@kieldercms1.open.ac.uk> > Content-Type: text/plain; charset="us-ascii" > > I would like to make point markers of varying sizes depending on their value > i.e. if it has a value of 10 then it would have a larger marker than if it had > a value of 1. This seems to be sort of possible via new > symbology>advanced>size scale field. However it only allows the values > themselves from the column not any transformation of them e.g. sqrt or log. > When producing this kind of map you often want to transform the numbers as they > are often of much too large a range to show with a simple linear scale.
Someone else might like to comment on this. I'm guessing that rather than offering a simple choice of using a log or sqrt scale, there will probably be a full "expression based" feature, similar to the expression based labelling Nathan has implemented. Personally I think this will be better. > So then tried the attribute table and field calculator to produce some new > fields with these transformed values and got caught up in how on earth to do it > and it did not seem to have log anyway. Log functions were added to trunk recently, so I think they would be available if you run the QGIS nightly builds. But they were not added to the context help at the same time - I filed a patch set yesterday which includes this. > Will simply produce these transformed > values in spreadsheet outside qgis and reimport them and give it another go, > but perhaps something for the wish list is to make it easier to do these > different sized markers and have different options for transformations as you > often don't know what kind of transformation would be suitable until you see > them on the map. Alister _______________________________________________ Qgis-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/qgis-user
