var lonC=lon1/2+lon2/2;
var latC=lat1/2+lat2/2;
var scaleX=(screenWidth-leftOffset-rightOffset)*(lon2-lon1);//Pixels in meter x
var scaleY=(screenHeight-topOffset-bottomOffset)*(lat2-lat1);//Pixels in meter y

var scale;//Scale equals minimal scale between scaleX and scaleY
if(scaleX<scaleY)
    scale=scaleX;
else scale=scaleY;