I'm trying to separate a specific area of lines in a topo shapefile in Qgis so I can import it into Civil 3D without it taking several centuries to load in the full file, however when I use the "split features" tool it takes forever just to cut one line, and trying to cut multiple lines just generates an error.
Also, since it's hard to explain what exactly I'm trying to do in a few words: just imagine having a square polygon and cutting out a smaller square from the center and deleting the rest (but in this sentence replace "square" with "topo line data").