Determining Best Map View for an array of locations

 

In the past it has been useful to be able to determine the best map view to display an array of locations. In the AJAX control there is a method call SetMapView which determines the best map view for an array of coordinates. The VEWS and Silverlight control do not have this functionality. A long time ago someone wanted to know how to determine the best map view before loading the map. This required us to calculate out the best map view ourselves using map scale information. I later implemented the same method when working with the VEWS so that I could geo-reference images from the Imagery service (http://rbrundritt.spaces.live.com/blog/cns!E7DBA9A4BFD458C5!488.entry). The method worked fairly well but I knew there was a better way to do this. When working with the Silverlight control I came across a situation where I needed this functionality again so I decided to create the updated method for determining the best map view using similar math that is used for the tiling system. This eliminated the need to maintain a list of scales for each zoom level and also reduce the amount of calculations that needed to be performed. Below is the updated algorithm for determining the best map view for a list of locations:

/// <summary> /// Calculates the best map view for a list of locations for a map /// </summary> /// <param name="locations">List of location objects</param> /// <param name="mapWidth">Map width in pixels</param> /// <param name="mapHeight">Map height in pixels</param> /// <param name="buffer">Width in pixels to use to create a buffer around the map. This is to keep pushpins from being cut off on the edge</param> /// <returns>Returns a MapViewSpecification with the best map center point and zoom level for the given set of locations</returns> public static MapViewSpecification BestMapView(IList<Location> locations, double mapWidth, double mapHeight, int buffer) {     MapViewSpecification mapView;     Location center = new Location();     double zoomLevel = 0;     double maxLat = -85;     double minLat = 85;     double maxLon = -180;     double minLon = 180;     //calculate bounding rectangle     for (int i = 0; i < locations.Count; i++)     {         if (locations[i].Latitude > maxLat)         {             maxLat = locations[i].Latitude;         }         if (locations[i].Latitude < minLat)         {             minLat = locations[i].Latitude;         }         if (locations[i].Longitude > maxLon)         {             maxLon = locations[i].Longitude;         }         if (locations[i].Longitude < minLon)         {             minLon = locations[i].Longitude;         }     }     center.Latitude = (maxLat + minLat) / 2;     center.Longitude = (maxLon + minLon) / 2;     double zoom1=0, zoom2=0;     //Determine the best zoom level based on the map scale and bounding coordinate information     if (maxLon != minLon && maxLat != minLat)     {         //best zoom level based on map width         zoom1 = Math.Log(360.0 / 256.0 * (mapWidth – 2*buffer) / (maxLon – minLon)) / Math.Log(2);         //best zoom level based on map height         zoom2 = Math.Log(180.0 / 256.0 * (mapHeight – 2*buffer) / (maxLat – minLat)) / Math.Log(2);     }     //use the most zoomed out of the two zoom levels     zoomLevel = (zoom1 < zoom2) ? zoom1 : zoom2;     mapView = new MapViewSpecification(center, zoomLevel);     return mapView; }