Planning a route from A to B on a map (and therefore in real life) is a very important skill.
Before you start you will have already learnt how to use a map with regard to reading it, coordinates, scale and symbols. You must be familiar with the use of the map and compass combined and be able to confidently identify points on the map using a coordinates system. If you cannot recognize what the symbols and information on the map represent then you will have no idea where your route will take you.
Having learnt all of this you must still take the time to plan your route. Often in a town or city it is all too easy to walk from A to B. If you know the local area you will not need to refer to a map. Perhaps your destination is clearly marked on street signs or maybe you can stop and ask directions of the locals.
In the 'middle of nowhere' this may not be the case. It is important that you can find your way from A to B. Merely knowing where A and B are may not be sufficient.
If you are planning a simple hike there are several points you need to consider.
How safe is the route?
Is the route easy to follow?
How long is the route?
Is it the most appropriate route?
Don't be fooled into the age old trap of 'shortest route is best'. This is often not the case. Being as the shortest route is effectively a straight line this will mean true cross-country walking. How would you like it if a party of scouts came trooping across your back garden on a short route?
It can also be more subtle. A short direct route may involve a lengthy walk along an A road (a main road). This may be dangerous as not all A roads are suitable for young people to walk on (indeed few are) and local knowledge will help you decide this. A walk which uses footpaths, quiet country roads or roads with a good pavement (although this may spoil the enjoyment of the walk) may be much more suitable.
Try not to go completely overboard though. A route that follows 372 different footpaths and encounters 765 junctions may be an absolute nightmare to follow. Unless you are absolutely certain of your position on the map at all times and are an expert map reader you may find yourself taking a wrong turn and wasting time (or worse, getting lost). Make sure the route is simple to follow, even at the expense of time.
How difficult is the route to follow physically? It is no use plotting a straight course across a mountain range, you will soon tire of needless walking up and down slopes. Learn to use all the information on the map and get used to the contour of the land. If your destination is on the other side of a mountain or hill and there are no obvious paths or landmarks you may well be better off going around the slope rather than up and over it. Not only will the going be easier and less tiring by following the base of the slope (often streams or a road will show you the easiest way around a slope) but you are less likely to veer off course if you use your map and compass carefully.
Safety is an important factor too. This may be as obvious as "do not walk along the motorway" which in any case is illegal. It may also mean something along the lines of "that area in town is renowned for fighting outside the pubs" and avoiding any dangers that you may be aware of. Steering clear of MOD property, shying away from industrial areas, making sure your route is not too isolated are all examples. For use in Scouting I would suggest that your route, wherever possible, never strays too far from 'help'. This may mean a town or farmhouse or maybe just a telephone. A longer route that veers slightly to stay near to 'help' will be much safer than the direct route 'across the middle of the desert'.
Planning an appropriate route can take into account your circumstances. If you are planning an incident hike for scouts a route that merely follows the local road from village to village will be of little challenge to the scouts. If you are planning a route for beginners one that involves many footpaths and changes of direction coupled with direct bearings across open ground will be far too difficult for the beginner to follow. A survival route may be planned to stay clear of villages and built up areas and only pass the odd farmhouse where the scouts can ask the farmer if they can pitch their tent in his field.
Many of the points that are important in map reading are followed by those in Orienteering. Orienteering involves using a map and compass to navigate to a number of points, often within a time limit.
Orienteers use the principle of attack points to navigate to a check point. Say for example a check point is at the junction of a stream and a track. Instead of trying to head cross country directly to the checkpoint the orienteer would use their map and compass to navigate straight to the stream say (any point on the stream). This need only be a rough and ready measurement. Once they hit the stream they turn and follow it to the junction whereupon they may find the checkpoint or take the time to make an accurate bearing.
Be sure to check out the excellent resources provided by Graham from the 12th Andover West.