Merge shapefiles using ogr2ogr and retrieve the attributes of both

Question

I have two shapefiles that I want merge (overlay/intersect) having in the destination the attributes of the two sources file.

ogr2ogr file_merged.shp tl_2010_us_uac10_conus_albersUA.shp
ogr2ogr -update -append file_merged.shp tabblock2010_10_pophu.shp -nln file_merged

In this way I obtain the polygons of the two shapes, but I lose the attributes of the tabblock2010_10_pophu.shp.

My final aim is then make an SQL statement where I can retrieve polygon in common in the both shapes.

Any suggestions??

Answer 1

Using GDAL >= 1.10.0 and its OGR Virtual Format, we can write a VRT file named, for example, merge.vrt (see Example: Union layer (GDAL >= 1.10.0)):

<OGRVRTDataSource>
    <OGRVRTUnionLayer name="unionLayer">
        <OGRVRTLayer name="source1">
            <SrcDataSource>source1.shp</SrcDataSource>
        </OGRVRTLayer>
        <OGRVRTLayer name="source2">
            <SrcDataSource>source2.shp</SrcDataSource>
        </OGRVRTLayer>
    </OGRVRTUnionLayer>
</OGRVRTDataSource>

and simply execute in order to simply preserve the attributes of both SHPs:

ogr2ogr merge.shp merge.vrt

Instead, if you want also exclude duplicate geometries from the result:

ogr2ogr merge_distinct.shp merge.vrt -dialect sqlite -sql "SELECT DISTINCT geometry, * FROM merge"

Answer 2

I wrote some downloadable code for that. A simple python program to combine shapefiles in many ways: http://gistncase.blogspot.com.au/2012/05/python-shapefile-merger-utility.html

By default performs the dbf schemes union and it adds an attribute filled with the source shapefile name, so you can recognize records.

This is the commandline for your needs:

python shapemerger.py -o file_merged.shp tl_2010_us_uac10_conus_albersUA.shp tabblock2010_10_pophu.shp

(you have to run it in a python environment with available ogr/gdal packages. I wrote some note about this above the code)