It is conducted on the image so that one will know the distribution of elements at each spot along the line plotted in the SEM image (from the line scan). In the end the results will be presented in a graph form. In my opinion, the graph is meaningless if the image is not shown.
When presenting the result of a line scan, one would place the graph beneath or beside the image for a better understanding of the element distribution.
Alternatively, you can conduct a EDS mapping but the results from the EDS mapping is from the whole area you have mapped while line scan is in point mode along the line you have plotted which usually would contain 5 or 10 points or more at different intervals(the intervals can be adjusted).
Ok ...but any how in the sample desired elements only(user desired element only to be present ) present then why it is so important@Rayappa Shrinivas Mahale
Line scan could deliver very desirable information about distribution of elements. But if do not need it, then line scan is not important, not improtant at all.