+44 (0)1451 820 181
skip to the main content area of this page
London Congestion Charge Zone

London Congestion Charge Zone

Detailed mapping of the London Congestion charge zone and a program module to determine if a vehicle location is within the London Congestion Charge Zone. The vehicle location and direction (if known) are used to determine which road a vehicle is on.

London Congestion Charge Zone Map (Larger sample)

In addition to using a simple geo fence area hit test, this module uses a vehicles Latitude/Longitude location and direction of travel (if known) to compute precisely which road a vehicle is on. This is then compared to a database of roads that are known to be within the London Congestion Charge Zone to determine whether or not the vehicle is within the London Congestion Charge Zone.

ISYS Know-How

Even with a 100% accurate vehicle location, vehicle direction is still necessary to determine which road a vehicle is on.

The majority of the map databases from Ordnance Survey and all the map databases from other suppliers (e.g. Navteq, TeleAtlas) contain road centreline coordinates, not road edge coordinates. In addition, coordinates for side roads are 'extended' so as to join the centre-line of the roads they intersect.

A vehicle travelling down a road will generally be to one side of the road centre-line and will cross these side road 'extensions' at every intersection. If the vehicle direction is not taken into account and you simply choose the ‘closest’ road to a vehicle location, then, in the vicinity of road intersections a side road 'extension' will invariably be closer.

By using the vehicle direction and comparing it to the road direction, it is possible to eliminate side roads as possibilities and correctly identify the road a vehicle is on.