Which is the best route to travel from A to B? - Route calculation
With the rising costs of fuel and the push to reduce exhaust emissions, a reduction in travel time will both save money and do less harm to the environment. GIS can be used in conjunction with an accurate road network to calculate the most efficient routes.
In its simplest form this could involve a simple travel from A to B. However in GIS you can define C, D or as many other locations that are required to be passed through. Such locations can be visited either in a strict order or using the most efficient route that passes through them in any order. You also have the option to return to base or not.
Within the road network data for each section has attributes such as length, speed (and so estimated travel time), quality, preference etc. The length of each road segment is very easy for GIS to calculate. Values such as speed are most important in determining travel times. A higher preference can be assigned for roads of a certain size, for instance to ensure that delivery lorries can traverse the road. Other values can be assigned to roads, if you want to avoid traffic (for example if you are planning a cycle route) by altering the preference values.
Using this information the quickest or the shortest route can be calculated. With more sophisticated systems this information can be updated with traffic condition such as accidents, congestion and road works etc.
The first picture shows two routes from Holyhead (H) to Beaumaris (B) shown in green and Amlwch (A) to Rhosneigr (R) in purple. This route was chosen so that the main roads were preferred to the smaller roads. Notice, especially in the A to R route, that the quickest route is not the shortest. This is due to the quality of the selected roads comparred to other possible roads.
The second image shows what happens when the priorities of the roads are switched. No longer are we after the quickest and most suitable route for lorry deliveries, this time the smaller quieter roads are preferred. This may be the case if you wish to follow a more rural route say on a pleasure trip or a bicycle. Notice again that, especially in the A to R route, that more direct route is selected.