Question

In the CLLocationManager class documentation, I find such explanation for the distanceFilter property:

This property is used only in conjunction with the standard location
services and is not used when monitoring significant location changes.

Can you please explain it?

Answer 1

In CLLocationManager, distanceFilter is used to notify changes when device has moved x meters. Default value is kCLDistanceFilterNone: all movements are reported.

From the docs

After returning a current location fix, the receiver generates update
events only when a significant change in the user’s location is
detected. For example, it might generate a new event when the device
becomes associated with a different cell tower. It does not rely on
the value in the distanceFilter property to generate events.

Start standard location services by calling the startUpdatingLocation
method. This service is most appropriate for applications that need
more fine-grained control over the delivery of location events.
Specifically, it takes into account the values in the desiredAccuracy
and distanceFilter property to determine when to deliver new events.
The precision of the standard location services are needed by
navigation applications or any application where high-precision
location data or a regular stream of updates is required. However,
these services typically require the location-tracking hardware to be
enabled for longer periods of time, which can result in higher power
usage.

That is why distanceFilter is used only in conjunction with the standard location services and is not used when monitoring significant location changes eg. desiredAccuracy or heading info.

This is because generally it is not really useful to know that a person has moved x meters. However, it is very valuable to know that a person has moved x meters in y heading with z accuracy.