[QGIS-trac] [Quantum GIS] #3253: Enhancement: option to "trim other layers to match"

[Quantum GIS]

#3253: Enhancement: option to "trim other layers to match"
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   Reporter:  Alister           |              Owner:  nobody       
       Type:  enhancement       |             Status:  new          
   Priority:  minor: annoyance  |          Milestone:  Version 2.0.0
  Component:  Symbology         |            Version:               
   Keywords:                    |   Platform_version:               
   Platform:  All               |           Must_fix:  No           
Status_info:  0                 |  
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 '''Task:'''
 It would be useful to be able to use a polygon to temporarily mask other
 layers.
 e.g. if you have a layer of boundaries for catchments (or provinces or
 something), to only display content within one particular catchment.

 '''Current way of achieving the task:'''
 I think the most flexible way to achieve this at the moment is:
 1. create a set of new mask layers, by subtracting each catchment from a
 polygon bigger than the area of interest.
 2. put these layers above everything else.
 3. only turn on the mask layer which corresponds to the area of interest.
 This method is fine for the work I do myself, because I work with only a
 small number of areas.  But it would not be practical with a large number.

 '''Proposed new feature'''
 I think the best way to do it would be to add an option "trim other layers
 to extent" (there is probably a better way of wording this - some people
 might think "extent" implies a rectangular area or something).
 This would allow the user to mask all map content outside a polygon layer
 or whatever subset of the layer is defined (by the query builder).
 A logical place for the option would be on the "general" tab in the "layer
 properties" dialogue, as this is where the layer subset is shown.

 N.B. sorry if I haven't picked the appropriate Component; I'm not sure
 which it should be.

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Ticket URL: <https://trac.osgeo.org/qgis/ticket/3253>
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