MKCoordinateSpanMake: why specify longitude and latitude?

Question

If the distance corresponding to one degree of longitude is a function of latitude, why should you specify longitudeDelta and latitudeDelta when calling MKCoordinateSpanMake in iOS MapKit? Moreover, how should I know what the correct ratio is?

Answer 1

You do not need to specify both parameters, and you do not need to pre-calculate the coefficient.

Both options are provided as a convenience if you have a previously saved range, or if you know the exact range that you want.

No matter what values ​​you pass, the map display will still adjust the range so that it matches the map viewing frame and matches the zoom level that it can display.

In fact, you can pass 0.0 for any parameter if you know or only about one of them. The map display will perform calculations and adjust the range as needed.

To find out what the adjusted range will be (or if you want to pre-calculate it), call the regionThatFits: method with an area containing the range, for example (10,0) .

In addition, after calling setRegion: mapView.region.span will also contain the adjusted range.