[Qgis-user] what is plotted

[Richard Duivenvoorde]

On 2011-09-15 17:32, M.E.Dodd wrote:
> If you have a map and you want to plot dots on it, each dot representing some quantity then what happens if you have several dots at exactly the same location i.e. the coordinates are identical.  Some possibilities are (a) just show the 'last' dot assuming qgis plots the dots one after another in order down the .csv file, (b) average the data then plot the average value at those coordinates, (c) something else, am sure there are other possibilities.  Am sure I have used gis systems in the past where both a and b have happened and its been difficult to tell what is going on.
> In my instance an mean value at each location is probably the most appropriate.

just for your information, Qgis has a renderer called 'Point
Displacement', it is distributed as a plugin called 'Displacement
Plugin' you have to either get it or otherwise only enable it (no
further calculations on both points).
It leave the two points intact, but renders them in a little circle
apart from each other. There are some possibilities to configure: like:
when are two points on 'identical location' (tolerance), the circle
style etc etc.

If the plugin is enabled, you can find it in the dropdown list of symbol
renderers (where 'Single Symbol', 'Categorized' etc are.

There is information about it in the docs:
http://download.osgeo.org/qgis/doc/manual/qgis-1.6.0_user_guide_en.pdf

Regard,

Richard Duivenvoorde