MKMapViewに全てのピンを表示させる。 ref: http://qiita.com/syou007/items/f6d190c08ee57cf6455f

file0.swift

            // 最低限の地図の大きさ
            let MINIMUM_MAP_SPAN = MKCoordinateSpanMake(0.002, 0.002)

            var topLeftCoord = CLLocationCoordinate2D(latitude: -90, longitude: 180)
            var bottomRightCoord = CLLocationCoordinate2D(latitude: 90, longitude: -180)

            // 2点間の計算を行う。
            // 現在地
            topLeftCoord.longitude = fmin(topLeftCoord.longitude, localCoordinate.longitude)
            topLeftCoord.latitude = fmax(topLeftCoord.latitude, localCoordinate.latitude)
            bottomRightCoord.longitude = fmax(bottomRightCoord.longitude, localCoordinate.longitude)
            bottomRightCoord.latitude = fmin(bottomRightCoord.latitude, localCoordinate.latitude)

            // ピンの位置
            topLeftCoord.longitude = fmin(topLeftCoord.longitude, pinCoordinate.longitude)
            topLeftCoord.latitude = fmax(topLeftCoord.latitude, pinCoordinate.latitude)
            bottomRightCoord.longitude = fmax(bottomRightCoord.longitude, pinCoordinate.longitude)
            bottomRightCoord.latitude = fmin(bottomRightCoord.latitude, pinCoordinate.latitude)

            var region = MKCoordinateRegion()
            region.center.latitude = topLeftCoord.latitude - (topLeftCoord.latitude - bottomRightCoord.latitude) * 0.5
            region.center.longitude = topLeftCoord.longitude + (bottomRightCoord.longitude - topLeftCoord.longitude) * 0.5

            // 端ギリギリにピンが立つのを避けるため少し広げる
            region.span.latitudeDelta = fabs(topLeftCoord.latitude - bottomRightCoord.latitude) * 1.1;
            region.span.longitudeDelta = fabs(bottomRightCoord.longitude - topLeftCoord.longitude) * 1.1;
            // 拡大しすぎの場合は最低限の縮尺にする
            region.span.latitudeDelta = fmax(MINIMUM_MAP_SPAN.latitudeDelta, region.span.latitudeDelta);
            region.span.longitudeDelta = fmax(MINIMUM_MAP_SPAN.longitudeDelta, region.span.longitudeDelta);

            self.mapView.setRegion(self.mapView.regionThatFits(region), animated: true)

file1.swift

self.mapView.showAnnotations(self.mapView.annotations, animated: true)