Re: [Qgis-user] advice needed - merge attributes
Hi, just to let you know - as of yesterday "Sum" is also available in the merge dialogue. Thanks to Jürgen Fischer! This means, if your areas before the merge were correct, using the sum operator you will get correct areas/lengths after the merge as well. Andreas PS: available in QGIS trunk On 09/17/2011 11:45 AM, David wrote: > Andreas - Thank you for your suggestions: at the moment the most important > variable is Area so I do need to add the areas of the merged polygons to get > a new total. The other variables in the list are names which I maybe have > to type in anyway. I'm going to try your idea and the suggestions I > received from other people. > David > > > > From: Andreas Neumann > To: qgis-user@lists.osgeo.org > Sent: Friday, 16 September 2011, 19:51 > Subject: Re: [Qgis-user] advice needed - merge attributes > > Hi, > > This should work. > > After selecting and merging the polygons a table should pop up where you > can select for each polygon the new attributes it should get. You can: > > * select one individual polygons attributes to be used or > * min > * max > * mean > * average > > However, I see that sum is not offered. Would you need the sum function? > > If yes, this should be rather easy to implement. > > Andreas > > > On 09/16/2011 04:08 PM, David wrote: >> Hi everyone, >> On a shapefile, given to me by the person who created it, I need to merge >> some polygons to make larger units.For example, select four adjacent >> polygons and use the merge tool and you get one large polygon. Great. >> However, on the attributes table what seems to happen is that instead of >> combining the various values (size, perimeter etc) three of the four >> polygons have disappeared leaving just one with its original data unchanged. >> Would some kind person tell me what I'm doing wrong? >> Thanks in advance. >> David Asquith >> UK >> >> >> >> ___ >> Qgis-user mailing list >> Qgis-user@lists.osgeo.org >> http://lists.osgeo.org/mailman/listinfo/qgis-user > > ___ > Qgis-user mailing list > Qgis-user@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/qgis-user ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] advice needed - merge attributes
Hi, This should work. After selecting and merging the polygons a table should pop up where you can select for each polygon the new attributes it should get. You can: * select one individual polygons attributes to be used or * min * max * mean * average However, I see that sum is not offered. Would you need the sum function? If yes, this should be rather easy to implement. Andreas On 09/16/2011 04:08 PM, David wrote: > Hi everyone, > On a shapefile, given to me by the person who created it, I need to merge > some polygons to make larger units.For example, select four adjacent > polygons and use the merge tool and you get one large polygon. Great. > However, on the attributes table what seems to happen is that instead of > combining the various values (size, perimeter etc) three of the four polygons > have disappeared leaving just one with its original data unchanged. Would > some kind person tell me what I'm doing wrong? > Thanks in advance. > David Asquith > UK > > > > ___ > Qgis-user mailing list > Qgis-user@lists.osgeo.org > http://lists.osgeo.org/mailman/listinfo/qgis-user ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
Re: [Qgis-user] advice needed - merge attributes
On Fri, 16 Sep 2011 15:08:45 +0100 (BST) David wrote: > Hi everyone, > On a shapefile, given to me by the person who created it, I need to > merge some polygons to make larger units. For example, select four > adjacent polygons and use the merge tool and you get one large > polygon. Great. However, on the attributes table what seems to > happen is that instead of combining the various values (size, > perimeter etc) three of the four polygons have disappeared leaving > just one with its original data unchanged. Would some kind person > tell me what I'm doing wrong? Thanks in advance. David Asquith UK Hello David, the merge tool doesn't update the attributes like size and perimeter automatically, you can use Geometry Tools > Export/Add geometry columns to update the values. They will be written in two columns called AREA and PERIMETER. If those columns exist, the values will be updated, otherwise they will be created. If you have area and perimeter stored in columns with another name, they will be ignored by this command. Another way is to open the shapefile, toggle editing, open Field Calculator (the little calculator at the right side of the buttons in attribute table) and update the fields for area and perimeter (see Manual section 4.7 "Field Calculator"). This second approach is a bit more complicated. Hope this helps, feel free to ask for more details if needed! Anne -- http://gis.cri.fmach.it/ghisla/ signature.asc Description: PGP signature ___ Qgis-user mailing list Qgis-user@lists.osgeo.org http://lists.osgeo.org/mailman/listinfo/qgis-user
