Display MKMapViewAnnotations within a map view's visible rect

Question

I\'m displaying an MKMapView inside a Path-style parallax table view header. To create the effect, the mapView bounds is larger than the area visible to the user. I need to set

Answer 1

If you're prepared to approximate the calculations you can do it using some clever scaling.

Your target area is 80 tall out of a mapView that is 380. Therefore you want a region that is 4.75x taller than the region calculated to fit your annotations. (0.25 extra above and 3.5 extra below).

First you need to get a region (or maprect, what ever you prefer working in) and make it the same proportions as your target viewable area. This is because a really wide and short region would not be touching the top and bottom of the viewable area and therefore multiplying its height would not make something that touched the top and bottom of your map view. So if viewable_height/viewable_width > annotations_height/annotations_width you should set the annotations_height to annotations_width * (viewable_height/viewable_width).

With that you then add 25% on to the north of the annotations box and 350% on to the south. You can do this by moving the center 212.5% (of the current height) south and increasing the vertical span by 475%.

Now, all of this is an approximation given that the world is sphere and we're not looking at a planar projection (i.e. 1 degree of latitude near the equator is drawn smaller than 1 degree near the poles). But if you wally want to be accurate you could look into scaling the numbers according to latitude and such. If you're only dealing with annotations on a city-sized scale you'll probably be ok.

Hope that helps.