Why a GPS is no substitude for map reading and navigation

I've loaded the detailed route I want to follow into a GPS as you describe. Surely if I follow the route line on the screen carefully I won't need to be able to read a map?

Wrong. Everyone heading into the hills should learn how to use both a map and compass. The first point is that a GPS is an electronic device and can fail. Your batteries may run flat, and even if you have plenty of spares, water may get into your GPS and damage it, you may not get a signal for some reason - the military occasionally even jam the devices as part of training exercises.

But even if your GPS could be guaranteed always to be working correctly, it is essential to be able to read your map. A proper map contains a vast amount of information on gradient, cliffs, crags, perhaps impassable streams and rivers, ridges, corries and sheltered glens. A GPS programmed with a route line cannot replace all this and make decisions for you. If you can't interpret a map to understand these features and the mountain's topography, you won't be able to see which routes are feasible, which are tricky or dangerous and what is the safest and fastest ways off the hill in an emergency. If you can't read a map (and use a compass), try to learn from experienced friends or colleagues, or consider going on a course – making the effort could save your life.