While the trace of the route is pretty straight-forward for open roads, the trace of a route where the road is flanked by tall buildings can look like this,
This can happen due to many reasons, where multi path effect due to the surrounding tall buildings is a major contributor. The signals received by the GNSS receiver from the satellites is interrupted by the tall buildings. This signal reflects and follows an alternative path to the receiver. The receiver thus receives two signals , with the same content but at different times. This confuses the receiver and thus it can skew the position, by a little.
To adjust for this skew in position, a complex algorithm had to be written to snap the vehicle to the nearest possible point on the road. Today it is possible by simply using the HERE Fleet Telematics Route Match API This API is a REST call which reads the raw route and returns a 'cleaned up' version of the route. To use this API, you need an app_id and app_code. If you don't have credentials yet, you can get them by signing up for free at the HERE Developer Portal