I need a union function for a lot of polygon layers (protected areas of all kind, nature, water etc.) comparable to the union function in ArcGIS. I have only the desktop version from ArcGIS and so it will only work on two layers.
I am looking for the same function in QGIS or another opensource GIS (openjump, gvsig….). I have tested MMQGIS and other functions in QGIS but I need union I think. I have merged layers in QGIS then worked my way with different spatial intersections in ArcGIS but thats all very complicated. I did union theme by theme in ArcGIS but in the end, I will have hundreds of themes so that is just impossible and union is just what I need.
The result should have all the attribute information of overlaying layers and the polygons should be split. An overlaying layer counts as an additional result and would be nice but not absolutely necessary as first impressions of how many different kinds of protected areas overlay. But in the end, it is most important that I do not lose any information for every little split polygon because I have to justify why or why not this exact polygon is convenient or not.
Best Answer
You can do this in QGIS, there is a Merge shapefiles to one function. This, compared to Union which only combines 2 layers, combines multiple shapefiles (selected either individually or by a directory) into one, contains additional results if there are any overlaps and no attribute fields are lost in the final layer. First install the fTools plugin:
Once installed, you should see a set of new functions in the Vector menu from the toolbar: