[Qgis-us-user] DBF table for SHP geo file

[Doug Newcomb]

Javier,
Here are a couple of links on the shapefile format.
You can also convert to geopackage, install the sqlite obdc connector , and
connect to the geopackage as a ODBC source in Access.



https://en.wikipedia.org/wiki/Shapefile#:~:text=The%20shapefile%20format%20is%20a,information%20system%20(GIS)%20software.&text=The%20shapefile%20format%20can%20spatially,wells%2C%20rivers%2C%20and%20lakes
.

http://www.esri.com/library/whitepapers/pdfs/shapefile.pdf

On Tue, Dec 29, 2020 at 5:28 PM <javier.valencia at vtgonline.com> wrote:

> Thank you so much Karsten,
>
> I am indeed creating the 3 files, in fact 5 files: Test.cpg, Test.dbf,
> Test.prj, Test.shp and Test.shx
>
> How are the SHP and DBF file related to each other? It cannot be the
> OBJECTID value since I when the values is nulled it still display the line
> but in a different color and with the OBJECTID column as NULL. Hmmm….
>
> What we are doing is merging smaller segment (city blocks) into larger
> segments (0.5 to 1 mile long) and the entire process is done on a separate
> database since there is a lot of programming going on to merge the segments
> and the data for the merged segment can be added, averaged, max or min
> selected or other calculations for over 100 columns/fields and all the
> programming to do this has already been done, we just need to display the
> map with segment already merged in on color and the segment to be merged on
> a separate color. It would take a lot of effort to reprogram it do it all
> in QGIS and at this time my expertise on Qgis is pretty limited…as you can
> tell. L
>
> The interesting part is when I edit records, the table does take changes
> to some other fields but it always sets the one field to NULL. I have tried
> taking a copy of just the DBF file and placing it on a separate directory
> and making the changes to that file with the same results. Also, the
> segments still display but when using the information tool the OBJECTID
> shows as NULL. Perhaps I can use this to show the segments with the OBJECTD
> column set to NULL as being already used and the ones with a values as
> available.
>
> I will play using MS Access to do the editing since I can easily connect
> to it and work with it from R:Base.
>
> I am new to this board and looks like this response goes to the Forum and
> to you.
>
> Again, thank you for the help, much appreciated.
>
>
>
> Best regards,
>
>
>
> Javier Valencia, PE
>
> 14315 S. Twilight Ln.
>
> Olathe, KS 66062
>
> Cell: 913-915-3137
>
>
>
> *From:* karsten [mailto:karsten at terragis.net]
> *Sent:* Tuesday, December 29, 2020 2:40 PM
> *To:* javier.valencia at vtgonline.com; qgis-us-user at lists.osgeo.org
> *Subject:* RE: [Qgis-us-user] DBF table for SHP geo file
>
>
>
> Hi Javier,
>
>
>
> > >>  I was provide an application in ArcInfo SHP format and the data
> appears to be stored in a DBF file (Dbase)
>
> Yes it is in dbf format .
>
>
>
>  >>> The first column in the table is a field OBJECTID which I believe
> might hold the line geometric information
>
> Nope. The geometry is in the *.shp file , while the *.shx is the index
> that connects the. Thus, editing the *.dbf does not touch the geometries .
> So one 'shape* is a file is in fact (at a minimum)  the three files - the
> *.shp, a *.dbf and the *.shx file...
>
>
>
>  >>>  I created a subset of the map, Test.DBF, with just a few columns
> including the OBJECTID column and a columns called “merged” that I need to
> edit from an external application
>
> That could work if you actually used a selection in QGIS to do this and
> have the saved that selected trifecta of the files  Test.shp, Test.dbf
> and Test.shx . If you only created  test.dbf instead that will not work. In
> that case recreate a new subset with those 3 files mentioned above (cerate
> selection then save layer (only selected) to a new shape file)
>
>
>
>  >>>  I ATTACH the Test.dfb table using an external database (R:Base) and
> I can see the column data just fine, the “merged” column show all values as
> NULL.
>
> When I change the value of “merged” from NULL to “Y” either via a grid or
> command, it changes it correctly but also changes the value of OBJECTID to
> NULL. When I open the map in QGIS and enable the layer “Test”, the lines
> still display but now the column OBJECT ID shows as NULL.  >>>
>
> I am not exactly sure how you are doing that in detail but in QGIS one can
> not usually edit joined data from another source (like other dbf files join
> on an id field, or joined xls(x) Excel files or csv data that where joined.
> The way to do it is to either
>
>
>
> 1.) edit the data outside QGIS and then join that table to the shape file
> it in QGIS (use the join tab) , or
>
>
>
> 2.) join the data in QGIS and then save the entire dataset (with those
> joined data) to a new shape file. If going that second route one can then
> edit the data easily inside QGIS. One good way to edit the data in QGIS is
> also using the field calculator - see here e.g.
> https://docs.qgis.org/3.16/en/docs/user_manual/working_with_vector/attribute_table.html?highlight=calculator#using-the-field-calculator .
>
>
>
>
> Cheers
>
> Karsten
>
>
>
> www.terragis.net
>
>
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