[Qgis-user] move 4 concentric circles from a position to

[Garth Fletcher]

Azzurra Lentini wrote:
> I must draw four different  concentric circles (with different sizes and
> same center) in many different positions: about these positions I know the
> center of the circles (shape file of points).


In Layer Properties > Symbology of your points shape file:
For Marker you could specify an Ellipse Marker and set
its size to the desired size in Map Units.
You can have multiple markers, so you could have 4 of such Ellipse
Markers, each with it own size.

Downside is that those concentric circles will only show in the
display and/or PDFs, but are not a separate shape layer of their own.
Depends what you need them for.

I've used a similar approach to display error bounds (95%) for
GSP'ed points.  There are 3 error ellipse arguments provided from
CSRS-PPP for post-processed points, which are used in expressions for:
   data	       Setting   Expression
  major axis    Width     "er_maj" *2
  minor axis    Height    "er_min" *2
  orientation   Rotation  "er_az"+90

Works a treat!
-- 
Garth Fletcher