[GIS] Copying fields from one layer to another in QGIS

layersqgisshapefile

I am new to QGIS. I need to create hundreds of shapefile layers with the same fields but different points and attribute values:

The first shapefile one I created with 12 fields (columns).
To create the second, I duplicated the first one.
Unchecked the first one to guarantee its safe.
In the attribute table, deleted all the points of the second since
the only thing important here is to keep the fields titles.
Start to map new points with its new attributes.

After click on save layer edits, all my points on the first layer are gone. I can not understand why the points and data on the first layer are being deleted.

Best Answer

Duplicating the layer in QGIS Canvas does not mean creating a new shapefile in your hard disk (HDD), you are still referencing to the same shapefile in your HDD. To create a new shapefile you need to right-click -> Export -> Save feature as and create a new shapefile.

Before exporting to a new shapefile, you can uncheck the fields that you do not need and check the fields the you want to keep in the new shapefile

Related Solutions

[GIS] Copying features from one attribute table to another using QGIS

There are more elegant ways to do this with joins, etc., but as an ad-hoc one off, one simple approach that should work is:

Export the original layer as a csv, but making sure under Layer Options you get the geometry exported AS_WKT. Your csv file should now consist of one line per feature, with the feature attributes as column, plus an extra first column called WKT representing the feature geometry as a text string in your chosen CRS.
You or others can change, even add/subtract rows, in Excel. Keep the column names (=attribute names) unchanged. You can theoretically change the geometry by editing the WKT string, but this is unlikely to be useful.
Import the edited csv as delimited text, making sure the importer Geometry Definition is set to WKT and pointed at the WKT field (which should be automatic). Make sure the geometry CRS is the same used for the export.
Re-export the imported csv layer in your desired spatial file format (shapefile if you must, or into a geopackage or whatever), probably the same as the original format.
Use the changeLayerSource plug-in to repoint the original layer at the new file from the previous step. If you indeed did not change the layer names, your styling etc will be preserved.

The above will implicitly (by sliding the new file in place of the old file) replace all of the old features with the edited ones, and so won't create duplicates. However, it also carries risks - you could munge stuff you didn't intend to touch if you're careless. If you need to be fancier, for instance you want to treat new features, updated features, and deleted features differently, then you will have to creatively use joins, or SQL.

The important elements for success above are to handhold QGIS to make sure the geometry is exported and then reimported, to make sure the CRS stays the same, and to ensure the data attribute names / column labels are unchanged.

Appending field from one layer into a different layer in QGIS

Version A: Join attributes by location

Use Menu Processing / Toolbox / Join attributes by location. Settings to make (red highlighted on the screenshot):

Set Y_data as Base layer and All data shapefile as Join layer
Check the box next to intersects
For Join type, select Take attributes of the feature with largest overlap only (one-to-one).

Optional settings (yellow on the screenshot):

Fields to add (leave empty to use all fields): select the ID-field.
Optionally, you can set a Joined field prefix to better distinguish the initial attributes from the ones added by the join operation.

Version B: field calculator

You could also create a new field with field calculator on the layer Y_data and this expression:

attribute( 
     get_feature_by_id( 
        'All_data_shapefile',
        array_first (
            overlay_equals( 
                'All_data_shapefile', 
                $id
            )
        )
    ),
    'id'
)

Best Answer

Related Solutions

[GIS] Copying features from one attribute table to another using QGIS

Appending field from one layer into a different layer in QGIS

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