[GIS] Problem Merging multiple shapefiles with different CRS in QGIS

mergeqgisshapefile

I am trying to merge multiple shapefiles into one, but I encounter one error, not all of my shapefiles end up merged. I am able to load all of my shapefiles but when I attempt to merge them, the merged attribute table contains all the information that it should but not all the shapefiles show-up. I made sure to change the the headings in the attribute tables that I want merged.

I have tried to use a number of tools (Merge Shapefiles to One, MMQGIS Combine etc.) but the problems seems to be that some of my shapefiles are projected differently. I have tried to change the coordinate reference system under Properties but after I save the file, the shapefile disappears. I have also found a guide to use GRASS to change the projection but I was not able to follow it.

Best Answer

Try do this:

Set Settings>CRS>"Automatically enable on the fly reproject..." and "Prompt for CRS"
Set CRS EPSG:4326 for your project
Open your merged EPSG:26917 .shp file and if will be prompted set EPSG:26917. You wouldn't be prompted if this vector has .prj file.
After that you will have reprojected .shp file from EPSG:26917 to EPSG:4326
Save this layer AS...ESRI file and select CRS as EPSG:4326
Remove old layers with EPSG:26917.
Click right mouse button to reprojected layer in legend window and "Zoom to layer".
Now you can try merge them all.

Possibly you can use ogr2ogr tool, look at last answer in this post: GDAL OGR2OGR

Update: I downloaded the data from the link and swapped them by description. Look at content of .prj files (open with notepad). After reprojection content should be like ..."GCS_WGS_1984"... not "NAD_1983_UTM_Zone_17N" Link to reprojected data

Related Solutions

[GIS] Merging shapefiles with GeoTools

Shapefiles in GeoTools are not mutable - the only way to change the schema of the shapefile is to read it in and write it back out to a new file with the modified schema.

To merge heterogeneous shapefiles you will need to read the schema of each file you want to import and then create a new schema that contains each attribute in those schemas. Then for each file read in the features and convert them to the new schema and write it back out to the new file.

Merge Shapefiles with Attributes Using PyQGIS – How to

OK here's the answer. I have discovered the processing toolbox from which there was a simple solution: As per http://qgis.org/de/docs/user_manual/processing/console.html

From the console you can get a list of all the algorithms available which contain the word "merge" by typing:

import processing
processing.alglist("merge")

Then you could find out how to use the most appropriate function with:

processing.alghelp("qgis:mergevectorlayers")

Then simply use the algorithm in your script as follows:

processing.runalg("qgis:mergevectorlayers", layer1, layer2,"outputfilename.shp")

On the other hand manually merging shapes may still be useful. For those who still want to manually copy features from an input layer into some destination layer with attributes you need to first make sure the destination layer has those fields.

old_attribute_List = input_layer.dataProvider().fields().toList()
new_attribute_List=[]
for attrib in old_attribute_List:
  if destination_layer.fieldNameIndex(attrib.name())==-1:
    new_attribute_List.append(QgsField(attrib.name(),attrib.type()))
destination_layer_data_provider.addAttributes(new_attribute_List)
destination_layer.updateFields()

Then to manually copy over the features you can do:

destination_layer.startEditing()
cfeature = QgsFeature()
cfeatures=[]
xfeatures = input_layer.getFeatures()
for xfeature in xfeatures:
    xgeometry = xfeature.geometry()
    #GEOMETRY TRANSFORM GOES HERE IF DESTINATION CRS DIFFERS FROM INPUT CRS
    cfeature_Attributes=[]
    cfeature_Attributes.extend(xfeature.attributes())
    cfeature.setGeometry(xgeometry)
    cfeature.setAttributes(cfeature_Attributes)
    cfeatures.append(cfeature)
destination_layer_data_provider.addFeatures(cfeatures)
destination_layer_data_provider.commitChanges()

Best Answer

Related Solutions

[GIS] Merging shapefiles with GeoTools

Merge Shapefiles with Attributes Using PyQGIS – How to

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