[Qgis-user] size of marker

[Anita Graser]

Hi Dodd,

Try deviding by 100.0 instead of 100. That way at least you should get
decimal results.

Did you try to write the column name like this: "DBH(mm)"/100.0

The way I understand it, this function simply multiplies the symbol base
size with the value in the attribute.

Best wishes,
Anita


On Wed, Mar 7, 2012 at 4:51 PM, M.E.Dodd <m.e.dodd at open.ac.uk> wrote:

>  I would like to set the size of point marker in qgis to be controlled by
> its data i.e. if the value is larger then the marker itself is larger.
> This appears to be possible in e.g. new symbology>advanced>size scale
> field, also possible to get to this other ways.  However its not clear how
> the value in the column affects the size, bigger numbers give bigger
> markers but no idea how much bigger or what the numbers in the column mean
> for the size, the particular numbers I had in the column gave huge markers
> totally unsuitable for the map.
> So I then tried to alter the numbers by creating extra column in the
> attributes table using the field calculator to divide the numbers by 100.
> Firstly this failed because the column title was DBH(mm), it seems the ()
> are not allowed. so I then changed name of column to dbh (in an external
> editor as I could not do it in the attributes table itself) which then
> allowed me to divide the numbers by 100.  However the new column only
> showed one figure so e.g. 180/100 = 1 not 1.8 even though that new column
> was width 10 precision 2, actually it showed number 1 whatever values I set
> for width and precision.
> Not sure if any of this is a bug but these potentially very useful
> functions don’t seem to quite work.
>
>
>
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