Line graphs. Line graphs commonly show data over time. In this example, from 1990 to 2006. With line graphs, it is also quite easy to identify trends – that is, the general direction of movement. In this example we can see that production increased, then decreased, increased again and then stabilised. In the IELTS test, line graphs compare at least two and up to five different categories. In this example, we are given only production and sales.