When you navigate the inland waters using a conventional paper chart, you lay out the chart on a table and compare the land features on the chart with what you see outside the boat. Then from knowing where you are currently, you select a course to where you intend to go. With GPS, the electronic chart shows the current position of the boat on the chart display. The paper chart is sufficiently large to make out the distant land points and markers to be able to know which way to head. And even if the distant vision is obscured, you can select a compass bearing to follow.

When using a laptop computer, however, the screen displays only a small portion of the larger paper chart. The range of vision on the screen is usually not sufficient to adequately determine the heading between distant land points. So it is necessary to plot a course line on the computer, before actually running the course. Then you steer to the course line. Drawing the course can be done at home before the cruise or aboard the boat just before the cruise. But to effectively use the laptop computer, one needs to plot a course line and then steer to follow that line. I have even modified the course line while under way to account for changes in plans.