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If the values to be displayed are large, it may help to use map
units instead of millimeters. This wouldn't be necessary if QGIS
allowed more decimals for 'Size' (option only available with 'Single
symbol' style). Users shouldn't be forced to create new variables,
in order to achieve what they want. Inexperienced users are scared
off and files get polluted this way. <br>
<br>
There is another problem with this technique. The user has no
choice, like in old symbology, between scaling the diameter or the
area of the symbol. The latter is most common for thematic maps,
especially if the range of values is large. This could be
circumvented by adding additional fields (using the square root),
but in my opinion that shouldn't be necessary.<br>
<br>
Sake Wagenaar<br>
<br>
Op 7-3-2012 16:51, M.E.Dodd schreef:
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<div>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.</div>
<div>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.</div>
<div>Not sure if any of this is a bug but these potentially very
useful functions don’t seem to quite work.</div>
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