I have a lines layer (a contour map of mean annual precipitation in Africa) that I want to clip to a polygon layer (shape of the African continent). However every time I use the clip tool (Vector-->Geoprocessing tools-->Clip), only an empty shapefile without attributes is created.
After looking at other questions in the site, I've already addressed two potential issues: (1) I've put the layers and the project in the same Coordinate Reference System (EPSG: 4326 - WGS 84) and (2) I converted the lines layer from multipart to singleparts after seeing this solved the problem for another user.
Something else to note, and I'm not sure if it even makes a difference: the lines vector layer was converted from a raster file using Raster-->Extraction-->Contour.
Below are a couple screenshots to add context:
I found a solution by clipping the original raster file using the Africa polygon as a mask. I then converted that clipped raster file to a contour map and it solved my problem. As @ChrisW pointed out below, there was a lot of data off the coasts and I may have not waited long enough for original file to process (i.e., 40+ hours).