The intersect operation is one of the many overlay operations. When intersecting layer A with a layer B the result will include all those parts that occur in both A and B. In this post I'm going to compare the results of the ArcGIS Intersect tool with the corresponding operation in 3 other GIS packages. The reason why did this was that I noticed that the output from ArcGIS contains more features then I expected when dealing with overlapping geometries. This is usually not a problem but it becomes one when you have lots of overlapping geometries.
To test the code I prepared 2 shapefiles. One with a long small polygon and the other one with 3 overlapping rectangles (see image below).
When intersecting with ArcGIS (version 9.2 and 9.3 tested) the output looks like below. As you can see in the attribute table the result contains 9 polygons.
To be able to do the intersect operation with uDig I had to install the Axios Spatial Operations Extension. You can install this extension by clicking Help -> Find and install from the menubar. With Quantum GIS I needed to enable the ftools plugin to enable the geoprocessing functionality. The results of the 3 used open source GIS packages where the same. Only 3 features where created in the output shapefile. For completeness I added the screenshots of the results.
Quantum GIS :
Have any comments or questions ? Let me know !