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I need to clip a large and very detailed .shp file in QGIS showing environmental data similar to a temperature map. Is there something like the very simple crop tool alike in photoshop where you can drag a rectangle over an area of interest and crop the shapefile to this area only?

I do have an additional shape file of neighborhoods/districts that I could also use for cropping but I do not know how to specify "extract a shp/kml only within the borders of district X, row xxxxx in the attribute table of districts.shp"

How can I extract the data primitively within a rectangle of choice or per district?! I need smaller pieces from the large map that has been provided by an environmental geo-institute to be implemented into an mobile Application (Android) to view the quite heavy data in a lighter way.

I made some screenshots of the data and posted them here: http://merglindev.wordpress.com/2012/10/22/extracting-districts-from-big-shapefile-data/. You can see the districts and the data layers. I need to have every district as a separate file / separately export every dataset per district to kml.

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You say you have a shapefile with appropriate regions, so you can use that for cutting. In the parlance of QGIS, it sounds like you are after Vector->Geoprocessing Tools -> Clip. If you need to assign the data from the input layer to smaller units in the region layer, you could intersect or union instead, in the same menu.

edit (by Kurt): here is an image for clarification: enter image description here yellow: input layer (china) green: clipmask-layer violett: clipped output-layer

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just make sure, that both layers (original layer and layer, which you use for clipping) use the same projection (crs) – Kurt Oct 21 '12 at 22:45
if i choose input vector layer "my_road_geodata" and use as a intersect layer "districts_2011" it processes a while but i don't see the difference to the original. "Union" just crashed my QGIS :( In the end I would like to export just one district x in combination with the "my_road_geodata" - is there any tutorial out there? – birgit Oct 21 '12 at 22:46
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Are you saying you are clipping a line (road) layer with a polygon layer? And are you after just ONE polygon area for your output, or multiple? – ako Oct 21 '12 at 23:47
It is not a line layer. The "my_road_geodata" shows zones of noise pollution in the form of filled polygons, like in this webapp si2.nl/eu-kaarten/rdam - when cutting it by districts I just want to get the same map but cut in small puzzle pieces... so extracting the areas one by one and saving them in a file like district01 district02 ... would be what I am aiming for – birgit Oct 22 '12 at 8:14

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